Glass substrate for flat panel display and manufacturing method thereof

ABSTRACT

A flat panel display glass substrate includes a glass comprising, in mol %, 55-80% SiO 2 , 3-20% Al 2 O 3 , 3-15% B 2 O 3 , and 3-25% RO (the total amount of MgO, CaO, SrO, and BaO). The contents in mol % of SiO 2 , Al 2 O 3 , and B 2 O 3  satisfy a relationship (SiO 2 +Al 2 O 3 )/(B 2 O 3 )=7.5-17. The strain point of the glass is 665° C. or more. The devitrification temperature of the glass is 1250° C. or less. The substrate has a heat shrinkage rate of 75 ppm or less. The rate of heat shrinkage is calculated from the amount of shrinkage of the substrate measured after a heat treatment which is performed at a rising and falling temperature rate of 10° C./min and at 550° C. for 2 hours by the rate of heat shrinkage (ppm)={the amount of shrinkage of the substrate after the heat treatment/the length of the substrate before the heat treatment}×10 6 .

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to glass substrates for flat paneldisplays and methods for manufacturing the glass substrates.

2. Related Background Art

Flat panel displays with small thickness and low power consumption, suchas a thin film transistor (TFT) liquid crystal display and an organicelectroluminescence (EL) display, have in recent years been employed asdisplays for mobile devices and the like. These displays typicallyinclude a glass substrate.

There are the following types of TFTs: an amorphous silicon (α-Si) TFT;and a polysilicon (p-Si) TFT. The p-Si TFT is advantageous over the α-SiTFT in terms of screen resolution, display durability, display thicknessand weight, and power consumption, and the like, i.e., the p-Si TFT canprovide a beautiful screen with a higher resolution, a display with ahigher durability, a display with a smaller thickness and a lowerweight, and lower power consumption. Conventionally, however, a hightemperature treatment is required in production of the p-Si TFT.Therefore, the glass substrate undergoes heat shrinkage and heat shockduring production of the p-Si TFT, and therefore, glass other thansilica glass cannot be employed. As a result, it is difficult to applythe p-Si TFT to a liquid crystal display.

However, the low-temperature polysilicon (LTPS) TFT, for which the heattreatment is performed at lower temperature, has in recent years beendeveloped, and therefore, the p-Si TFT has been applicable to the flatpanel display. As a result, the display of a small device (e.g., amobile device, etc.) can have a beautiful screen with a high resolution.

Note that the heat treatment in production of the p-Si TFT stillrequires a temperature of as high as 400 to 600° C. Most of theconventional glass substrates for displays do not have a sufficientlyhigh strain point, and therefore, are likely to undergo significant heatshrinkage due to the heat treatment in production of the p-Si TFT,leading to a non-uniform pixel pitch. Moreover, in recent years, therehas been a demand for higher and higher resolutions. Therefore, in orderto reduce such a non-uniform pixel pitch, it is highly desirable toreduce the heat shrinkage of the glass substrate during production ofthe display. Conventionally, glass substrates for displays which havebeen developed in view of the heat shrinkage problem have been reported(JP 2002-3240A, JP 2004-315354A, and JP 2007-302550A).

SUMMARY OF THE INVENTION

Here, the heat shrinkage of the glass substrate can be reduced byincreasing characteristic (low-temperature viscosity characteristic)temperatures in the low temperature viscosity range, typified by a glasstransition temperature (hereinafter referred to as a “Tg”) and a strainpoint (the “Tg and strain point” will be described hereinafter astypical examples of the low-temperature viscosity characteristictemperature in this specification). However, if the composition of aglass is modified only for the purpose of increasing the Tg and strainpoint of the glass, the devitrification resistance of the glass islikely to deteriorate. If the devitrification resistance deteriorates,i.e., the devitrification temperature increases, so that the liquidusviscosity decreases, the flexibility of the production method alsodecreases. If the devitrification temperature increases, so that theliquidus viscosity decreases, it is difficult to produce the glasssubstrate, for example, by the overflow downdraw process.

Therefore, it is an object of the present invention to provide a glasssubstrate for flat panel displays which simultaneously has a high Tg andstrain point and good devitrification resistance and in which anon-uniform pixel pitch does not occur even if the glass substrate isused in a display to which the p-Si TFT is applied.

A first example flat panel display glass substrate on which a p-Si TFTcan be formed according to the present invention includes a glasscomprising, as expressed in mol %;

55-80% SiO₂;

3-20% Al₂O₃;

3-15% B₂O₃; and

3-25% RO (the total amount of MgO, CaO, SrO, and BaO)

wherein

in the glass, the contents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfy arelationship (SiO₂+Al₂O₃)/(B₂O₃)=7.5-17,

the strain point of the glass is 665° C. or more, and

the devitrification temperature of the glass is 1250° C. or less, and

the glass substrate has a heat shrinkage rate of 75 ppm or less.

The ratio of heat shrinkage is calculated from the amount of shrinkageof the glass substrate measured after a heat treatment which isperformed at a rising and falling temperature rate of 10° C./min and at550° C. for 2 hours by:the ratio of heat shrinkage (ppm)={the amount of shrinkage of the glasssubstrate after the heat treatment/the length of the glass substratebefore the heat treatment}×10⁶

The “ratio of heat shrinkage” as used hereinafter has the same meaning.

A second example flat panel display glass substrate on which a p-Si TFTcan be formed according to the present invention includes a glasscomprising, as expressed in mol %;

55-80% SiO₂;

3-20% Al₂O₃;

3-15% B₂O₃; and

3-25% RO (the total amount of MgO, CaO, SrO, and BaO)

wherein

in the glass the contents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfy arelationship (SiO₂+Al₂O₃)/(B₂O₃)=8.45-17.0, and

the devitrification temperature of the glass is 1250° C. or less, and

the glass substrate has a heat shrinkage rate of 60 ppm or less.

According to a third aspect of the present invention, a flat paneldisplay glass substrate on which a p-Si TFT can be formed includes aglass comprising, as expressed in mol %;

55-80% SiO₂;

3-20% Al₂O₃;

3-15% B₂O₃; and

3-25% RO (the total amount of MgO, CaO, SrO, and BaO)

wherein

in the glass the contents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfy arelationship (SiO₂+Al₂O₃)/(B₂O₃)=7.5-17,

the strain point of the glass is 665° C. or more, and

the devitrification temperature of the glass is 1250° C. or less, and

the glass substrate has a heat shrinkage rate of 75 ppm or less after aheat treatment in which the glass substrate is kept at Tg for 30 min,then cooled at a rate of 100° C./min until the temperature thereofreaches Tg−100° C., then cooled until the temperature reaches roomtemperature, and then kept at 550° C. for 2 hours, wherein a rising andfalling temperature rate is 10° C./min.

A first example method for manufacturing a flat panel display glasssubstrate on which a p-Si TFT can be formed according to the presentinvention, includes:

a melting step of melting a glass material for a glass comprising, asexpressed in mol %, 55-80% SiO₂, 3-20% Al₂O₃, 3-15% B₂O₃, and 3-25% RO(the total amount of MgO, CaO, SrO, and BaO), with the contents in mol %of SiO₂, Al₂O₃, and B₂O₃ satisfying a relationship(SiO₂+Al₂O₃)/(B₂O₃)=7.5-17, the strain point of the glass being 665° C.or more, and the devitrification temperature of the glass being 1250° C.or less, to produce a molten glass;

a forming step of forming the molten glass into a glass plate; and

an annealing step of annealing the glass plate,

where

the glass plate has a heat shrinkage rate of 75 ppm or less.

A second example method for manufacturing a flat panel display glasssubstrate on which a p-Si TFT can be formed according to the presentinvention, includes:

a melting step of melting a glass material for a glass comprising, asexpressed in mol %, 55-80% SiO₂, 3-20% Al₂O₃, 3-15% B₂O₃, and 3-25% RO(the total amount of MgO, CaO, SrO, and BaO), with the contents in mol %of SiO₂, Al₂O₃, and B₂O₃ satisfying a relationship(SiO₂+Al₂O₃)/(B₂O₃)=8.45-17.0 and the devitrification temperature of theglass being 1250° C. or less, to produce a molten glass,

a forming step of forming the molten glass into a glass plate, and

an annealing step of annealing the glass plate,

wherein

the glass plate has a heat shrinkage rate of 60 ppm or less.

A first example flat panel display glass substrate according to thepresent invention includes a glass comprising, as expressed in mol %;

55-80% SiO₂;

3-20% Al₂O₃;

3-15% B₂O₃; and

3-25% RO (the total amount of MgO, CaO, SrO, and BaO)

wherein

in the glass the contents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfy arelationship (SiO₂+Al₂O₃)/(B₂O₃)=7.5-17,

the strain point of the glass is 665° C. or more, and

the devitrification temperature of the glass is 1250° C. or less, and

the glass substrate has a heat shrinkage rate of 75 ppm or less.

A second flat panel display glass substrate according to the presentinvention includes a glass comprising, as expressed in mol %;

55-80% SiO₂;

3-20% Al₂O₃;

3-15% B₂O₃; and

3-25% RO (the total amount of MgO, CaO, SrO, and BaO)

wherein

in the glass the contents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfy arelationship (SiO₂+Al₂O₃)/(B₂O₃)=8.45-17.0, and

the devitrification temperature of the glass is 1250° C. or less, and

the glass substrate has a heat shrinkage rate of 60 ppm or less.

The glass substrate of the present invention can simultaneously haveboth a high Tg and strain point and good devitrification resistance.Therefore, according to the present invention, a glass substrate havingexcellent properties can be provided in which the heat shrinkage causedby a heat treatment during production of a display is reduced, andtherefore, the non-uniformity of the pixel pitch does not occur.

DETAILED DESCRIPTION OF THE INVENTION

A display glass substrate according to this embodiment includes a glasswhich comprises, as expressed in mol %, 55-80% SiO₂, 3-20% Al₂O₃, 3-15%B₂O₃, and 3-25% RO (the total amount of MgO, CaO, SrO, and BaO), wherethe contents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfy a relationship(SiO₂+Al₂O₃)/(B₂O₃)=7.5-17. Another display glass substrate of thisembodiment includes a glass which comprises, as expressed in mol %,55-80% SiO₂, 3-20% Al₂O₃, 3-15% B₂O₃, and 3-25% RO (the total amount ofMgO, CaO, SrO, and BaO), where the contents in mol % of SiO₂, Al₂O₃, andB₂O₃ satisfy a relationship (SiO₂+Al₂O₃)/(B₂O₃)=8.45-17.0. If therelationship (SiO₂+Al₂O₃)/(B₂O₃)=7.5-17, more preferably therelationship (SiO₂+Al₂O₃)/(B₂O₃)=8.45-17.0, is satisfied, the glasssubstrate of this embodiment can have an increased Tg and strain pointwhile maintaining good devitrification resistance. By the increase ofthe Tg and strain point, the amount of heat shrinkage occurring in aheat treatment during production of a display is reduced. If the amountsof SiO₂ and Al₂O₃ are simply increased and the amount of B₂O₃ is simplydecreased in order to increase the Tg and strain point, the meltingtemperature may increase, i.e., the meltability may decrease. However,if SiO₂, Al₂O₃, and B₂O₃ satisfy the above relationship, the decrease ofthe meltability can be reduced. In other words, the glass substrate ofthis embodiment can have an increased Tg and strain point whilemaintaining good devitrification resistance and good meltability.

The glass included in the glass substrate of this embodiment maycomprise 5% or less ZnO as an optional component. In this case, it ispreferable that the contents in mol % of SiO₂ and Al₂O₃ satisfySiO₂+Al₂O₃≧70%, more preferably SiO₂+Al₂O₃≧75%, and the contents in mol% of RO, ZnO, and B₂O₃ satisfy RO+ZnO+B₂O₃=7-25%.

The glass included in the glass substrate of this embodiment may have astrain point of 660° C. or more. In order to more reliably reduce theheat shrinkage during production of a flat panel display, the strainpoint is preferably 665° C. or more, more preferably 675° C. or more,even more preferably 680° C. or more, still even more preferably 685° C.or more, still even more preferably 690° C. or more, still even morepreferably 695° C. or more, and still even more preferably 700° C. ormore.

The meltability of a glass may be evaluated by glass temperature(melting temperature), where the viscosity is 10²⁵ dPa·s. The glassincluded in the glass substrate of this embodiment preferably has amelting temperature of 1680° C. or less. If the melting temperature is1680° C. or less, the glass substrate of this embodiment can have goodmeltability. If the melting temperature is excessively low, the Tg andstrain point are likely to be low. Therefore, in order to achieve a highTg and strain point, the melting temperature needs to be fairly high.Therefore, the melting temperature is preferably 1550-1650° C., morepreferably 1550-1645° C., even more preferably 1580-1640° C., still evenmore preferably 1590-1630° C., and still even more preferably 1600-1620°C.

The amount of heat shrinkage may be reduced by appropriately adjustingconditions under which a glass is produced in addition to theaforementioned adjustment of a glass composition. Specifically, when theglass is annealed, then if the glass is cooled at a necessarily andsufficiently low rate in a temperature region of Tg to Tg-100° C., theamount of heat shrinkage can be reduced. Therefore, in the glasssubstrate of this embodiment, by optionally adjusting the conditions forthe annealing as appropriate in addition to the aforementionedadjustment of a composition, the ratio of heat shrinkage can be causedto be 75 ppm or less, preferably 65 ppm or less, and more preferably 60ppm or less. If the ratio of heat shrinkage is 75 ppm or less,preferably 65 ppm or less, and more preferably 60 ppm or less, even whenthe glass substrate of this embodiment is employed in a display to whichthe p-Si TFT is applied, and moreover, the display has a highresolution, the non-uniformity of the pixel pitch can be sufficientlyreduced. In order to reliably reduce the non-uniformity of the pixelpitch, the ratio of heat shrinkage is preferably 55 ppm or less, morepreferably 50 ppm or less, even more preferably 45 ppm or less, stilleven more preferably 43 ppm or less, still even more preferably 40 ppmor less, and still even more preferably 38 ppm or less. In other words,the ratio of heat shrinkage is 0-75 ppm, preferably 0-65 ppm, morepreferably 0-60 ppm, even more preferably 0-55 ppm, still even morepreferably 0-50 ppm, still even more preferably 0-45 ppm, still evenmore preferably 0-43 ppm, still even more preferably 0-40 ppm, and stilleven more preferably 0-38 ppm. Note that, in order to cause the ratio ofheat shrinkage to be zero ppm, it may be necessary to perform theannealing for a considerably long time or perform a heat shrinkagereduction treatment (off-line annealing) after the annealing, leading toa reduction in productivity and an increase in cost. In view ofproductivity and cost, the ratio of heat shrinkage is, for example, 3-75ppm, preferably 5-75 ppm, more preferably 5-65 ppm, even more preferably8-55 ppm, still even more preferably 8-50 ppm, still even morepreferably 10-45 ppm, still even more preferably 10-43 ppm, still evenmore preferably 10-40 ppm, and still even more preferably 15-38 ppm.

The glass included in the glass substrate of this embodiment has adevitrification temperature of 1250° C. or less. If the devitrificationtemperature is 1250° C. or less, the glass included in the glasssubstrate of this embodiment can be advantageously easily formed by adowndraw process. As a result, the surface quality of the glasssubstrate can be improved, and the manufacturing cost of the glasssubstrate can be reduced. If the devitrification temperature isexcessively high, devitrification is likely to occur, i.e., thedevitrification resistance decreases. Therefore, the devitrificationtemperature of the glass substrate of this embodiment preferably 1230°C. or less, more preferably 1220° C. or less, even more preferably 1210°C. or less, and still even more preferably 1200° C. or less. On theother hand, in order to achieve properties of a substrate for flat paneldisplays, such as low heat shrinkage and low density, thedevitrification temperature of the glass included in the glass substrateis preferably 1050-1250° C., more preferably 1110-1250° C., even morepreferably 1150-1240° C., still even more preferably 1160-1230° C., andstill even more preferably 1170-1220° C.

The glass included in the glass substrate of this embodiment preferablyhas a liquidus viscosity of 10^(4.0) dPa·s or more, more preferably10^(4.5) dPa·s or more. If the liquidus viscosity is 10^(4.0) dPa·s ormore, the glass can be easily formed by a float process. If the liquidusviscosity is 10^(4.5) dPa·s or more, the ease of forming is furtherimproved. Therefore, if the liquidus viscosity is within such a range,the glass included in the glass substrate of this embodiment can beeasily formed by a downdraw process (particularly, the overflow downdrawprocess). As a result, the surface quality of the glass substrate can beimproved and the manufacturing cost of the glass substrate can bereduced. The liquidus viscosity is more preferably 10^(4.5)-10^(6.0)dPa·s, more preferably 10^(4.5)-10^(5.9) dPa·s, even more preferably10^(4.6)-10^(5.8) dPa·s, still even more preferably 10^(4.6)-10^(5.7)dPa·s, still even more preferably 10^(4.7)-10^(5.7) dPa·s, still evenmore preferably 10^(4.8)-10^(5.6) dPa·s, and still even more preferably10^(4.9)-10^(5.5) dPa·s.

Other properties of the glass included in the glass substrate of thisembodiment are preferably within the following ranges.

The average coefficient of thermal expansion within the range of100-300° C. of the glass included in the glass substrate of thisembodiment is preferably less than 37×10⁻⁷K⁻¹, more preferably no lessthan 28×10⁻⁷K⁻¹ and less than 36×10⁻⁷K⁻¹, even more preferably no lessthan 30×10⁻⁷K⁻¹ and less than 35×10⁻⁷K⁻¹, still even more preferably noless than 31×10⁻⁷K⁻¹ and less than 34.5×10⁻⁷K⁻¹, and still even morepreferably no less than 32×10⁻⁷K⁻¹ and less than 34×10⁻⁷K⁻¹. If thecoefficient of thermal expansion is excessively high, the heat shock orthe amount of heat shrinkage increases in the heat treatment duringproduction of a display. On the other hand, if the coefficient ofthermal expansion is excessively low, it is difficult to match thecoefficients of thermal expansion of peripheral materials, such as ametal and an organic adhesive, formed on the glass substrate duringproduction of a display, and therefore, the peripheral materials arelikely to come off the glass substrate. In the p-Si TFT productionprocess, rapid heating and rapid cooling are repeatedly performed, andtherefore, greater heat shock is applied to the glass substrate. Whenthe glass substrate is large, a temperature difference (temperaturedistribution) is likely to occur in the heat treatment step, leading toan increase in the probability of destruction of the glass substrate. Ifthe coefficient of thermal expansion is within the aforementioned range,thermal stress caused by a difference in thermal expansion can bereduced, resulting in a decrease in the probability of destruction ofthe glass substrate in the heat treatment step. Note that whenimportance is put on the matching with the coefficients of thermalexpansion of the peripheral materials, such as a metal and an organicadhesive, formed on the glass substrate, the average coefficient ofthermal expansion within the range of 100-300° C. of the glass includedin the glass substrate is preferably less than 55×10⁻⁷K⁻¹, morepreferably less than 40×10⁻⁷K⁻¹, even more preferably no less than28×10⁻⁷K⁻¹ and less than 40×10⁻⁷K⁻¹, still even more preferably no lessthan 30×10⁻⁷K⁻¹ and less than 39×10⁻⁷K⁻¹, still even more preferably noless than 32×10⁻⁷K⁻¹ and less than 38×10⁻⁷K⁻¹, and still even morepreferably no less than 34×10⁻⁷K⁻¹ and less than 38×10⁻⁷K⁻¹.

If the Tg is excessively low, the heat resistance decreases, and in theheat treatment step, the heat shrinkage increases. Therefore, the Tg ofthe glass substrate of this embodiment is preferably 720° C. or more,more preferably 740° C. or more, even more preferably 745° C. or more,still even more preferably 750° C. or more, still even more preferably755° C. or more, and still even more preferably 760° C. or more.

If the density is excessively high, it may be difficult to reduce theweight of the glass substrate, and therefore, it may be difficult toreduce the weight of a display. Therefore, the density of the glasssubstrate of this embodiment is preferably 2.6 g/cm³ or less, morepreferably less than 2.5 g/cm³, even more preferably 2.45 g/cm³ or less,still even more preferably 2.42 g/cm³ or less, and still even morepreferably 2.4 g/cm³ or less. In particular, in order to reduce theweight of the glass substrate for a flat display or an organic ELdisplay including the p-Si TFT, the density is preferably less than 2.5g/cm³, more preferably 2.45 g/cm³ or less, even more preferably 2.42g/cm³ or less, and still even more preferably 2.4 g/cm³ or less.

If the specific resistance of a glass melt is excessively low, then whena glass material is electrically melted, the value of a current requiredfor melting the glass material is excessively large. Therefore, theremay be constraints on equipment. Moreover, the electrode isdisadvantageously much consumed. On the other hand, if the specificresistance is excessively high, then when the glass material is melted,a current flows through heat-resistant bricks forming a melting bath,likely leading to damage to the melting bath. Therefore, the specificresistance at 1550° C. of the glass included in the glass substrate ofthis embodiment is preferably 50-300Ω·cm, more preferably 50-250Ω·cm,even more preferably 80-240Ω·cm, and still even more preferably100-230Ω·cm.

If the Young's modulus and specific modulus of elasticity (Young'smodulus/density) are excessively low, the glass substrate is bent orwarped by its own weight during production of a display, likely leadingto damage to the glass substrate. In particular, if the glass substrateis large (e.g., 2000 mm or more wide), the damage caused by the bendingor warp becomes significant. Therefore, the Young's modulus of the glasssubstrate of this embodiment is preferably 70 GPa or more, morepreferably 73 GPa or more, even more preferably 74 GPa or more, andstill even more preferably 75 GPa or more. The specific modulus ofelasticity of the glass substrate of this embodiment is preferably 28GPa or more, more preferably 29 GPa or more, even more preferably 30 GPaor more, and still even more preferably 31 GPa or more.

Next, components of the glass included in the glass substrate of thisembodiment will be described. Note that “mol %” is simply hereinaftershortened to “%”.

(SiO₂)

SiO₂ is a skeletal and essential component. If the amount of SiO₂ isexcessively small, the acid resistance may decrease, the Tg and strainpoint may decrease, the coefficient of thermal expansion may increase,and the buffered hydrofluoric acid (BHF) resistance may decrease. It mayalso be difficult to reduce the density. On the other hand, if theamount of SiO₂ is excessively large, the melting temperature may besignificantly high, and therefore, it may be difficult to melt and formthe glass. The devitrification resistance may also decrease. Also, whenthe glass is slimmed down, the etching rate cannot be sufficientlyincreased. Therefore, the SiO₂ content is preferably 55-80%, morepreferably 60-78%, even more preferably 62-78%, still even morepreferably 65-78%, and still even more preferably 65-75%. Note that whenthe glass substrate comprises only less than 3% SrO+BaO in order tofurther reduce the weight, the SiO₂ content is more preferably 67-73%,even more preferably 69-72%. In order to sufficiently increase theetching rate when the glass is slimmed down, the SiO₂ content is morepreferably 62-78%, even more preferably 62-73%, and still even morepreferably 64-70%. On the other hand, when the glass substrate comprises3% or more SrO+BaO, the SiO₂ content is more preferably 65-73%, evenmore preferably 66-71%.

(Al₂O₃)

Al₂O₃ is an essential component which reduces phase separating andincreases the Tg and strain point. If the amount of Al₂O₃ is excessivelysmall, the glass is likely to undergo phase separating. Also, the Tg andstrain point may decrease, so that the heat resistance may decrease, theratio of heat shrinkage may increase, and the Young's modulus maydecrease. Also, the rate of etching the glass cannot be sufficientlyincreased. On the other hand, if the amount of Al₂O₃ is excessivelylarge, the devitrification temperature of the glass increases, so thatthe devitrification resistance decreases, and therefore, the ease offorming deteriorates. Therefore, the Al₂O₃ content is preferably 3-20%,more preferably 5-18%, and even more preferably 5-15%. Note that whenthe glass substrate comprises only less than 3% SrO+BaO in order tofurther reduce the weight, the Al₂O₃ content is more preferably 7-13%,even more preferably 9-12%. In order to sufficiently increase theetching rate when the glass is slimmed down, the Al₂O₃ content is morepreferably 7-15%, even more preferably 9-14%, and still even morepreferably 10-14%. On the other hand, when the glass substrate comprises3% or more SrO+BaO, the Al₂O₃ content is more preferably 8-15%, evenmore preferably 10-14%.

(B₂O₃)

B₂O₃ is an essential component which reduces the viscositycharacteristic (high-temperature viscosity characteristic) temperaturein a high temperature region, typified by the melting temperature, toimprove the meltability (the “melting temperature” will be describedhereinafter as a typical example of the “high-temperature viscositycharacteristic temperature” in this specification). If the amount ofB₂O₃ is excessively small, the meltability may decrease, the BHFresistance may decrease, the devitrification resistance may decrease,and the coefficient of thermal expansion may increase. Also, the densitymay increase, so that it may be difficult to reduce the density. On theother hand, if the amount of B₂O₃ is excessively large, the Tg andstrain point may decrease, the acid resistance may decrease, and theYoung's modulus may decrease. Also, B₂O₃ evaporates during melting ofthe glass, so that the non-uniformity of the glass may becomesignificant, and therefore, a cord is likely to occur. Therefore, theB₂O₃ content is preferably 3-15%, more preferably 3-13%, and even morepreferably 3-10%. Note that when the glass substrate comprises only lessthan 3% SrO+BaO in order to further reduce the weight, the B₂O₃ contentis more preferably no less than 3% and less than 9.5%, even morepreferably no less than 3.5% and less than 9.2%, still even morepreferably no less than 4% and less than 8.9%, still even morepreferably 5-8.5%, and still even more preferably 6-8%. Moreover, inorder to prevent the increase of the devitrification temperature, theB₂O₃ content is more preferably 5-13%, even more preferably 5-12%, andstill even more preferably 6% to less than 10% (no less than 6% and lessthan 10%). On the other hand, when the glass substrate comprises 3% ormore SrO+BaO, the B₂O₃ content is more preferably 3-9%, even morepreferably 4-8%.

(MgO)

MgO is a component which improves the meltability. MgO is also acomponent which hardly increases the density compared with otheralkaline-earth metals. Therefore, if the MgO content is relativelyincreased, the density of the glass can be easily reduced. In the glasssubstrate of this embodiment, MgO is not essential. However, if MgO iscomprised, the meltability can be increased and the occurrence of chipscan be reduced. Therefore, MgO may be comprised. However, if the amountof MgO is excessively large, the Tg and strain point may decrease, theheat resistance may decrease, and the acid resistance may decrease.Also, the devitrification temperature may increase, i.e., thedevitrification resistance may decrease, and therefore, it may bedifficult to employ a downdraw process. Therefore, in the glasssubstrate of this embodiment, the MgO content is preferably 0-15%, morepreferably 0-10%. Note that when the glass substrate comprises only lessthan 3% SrO+BaO in order to further reduce the weight, the MgO contentis more preferably 0-5%, even more preferably 0% to less than 2% (noless than 0% and less than 2%), still even more preferably 0-1.5%, stilleven more preferably 0-1%, and still even more preferably 0-0.5%, andstill even more preferably, substantially no MgO is comprised. Notethat, as used herein, “substantially no MgO is comprised” means that MgOis not added as a material to the glass material, and the MgO content ispreferably 0.2% or less, more preferably 0.15% or less, and even morepreferably 0.1% or less. The phrase “substantially no X (X: apredetermined component) is comprised” has the same meaning. On theother hand, when the glass substrate comprises 3% or more SrO+BaO, theMgO content is more preferably 1-9%, even more preferably 2-8%.

(CaO)

CaO is a component which is effective in improving the meltability of aglass without rapidly increasing the devitrification temperature of theglass. CaO is also a component which increases the density more slowlythan other alkaline-earth metals. Therefore, if the CaO content isrelatively increased, the density of the glass can be easily reduced. Ifthe amount of CaO is excessively small, the meltability anddevitrification resistance are likely to decrease due to an increase inthe viscosity at high temperature. On the other hand, if the amount ofCaO is excessively large, the coefficient of thermal expansion is likelyto increase. For these reasons, the CaO content is preferably 0-20%,more preferably 0-18%. Note that when the glass substrate comprises onlyless than 3% SrO+BaO in order to further reduce the weight, the CgOcontent is more preferably 3.6-16%, even more preferably 4-16%, stilleven more preferably 6-16%, still even more preferably more than 7% andno more than 16%, still even more preferably 8-13%, and still even morepreferably 9-12%. On the other hand, when the glass substrate comprises3% or more SrO+BaO, the CaO content is more preferably 0-10%, even morepreferably 0-5%, and still even more preferably 0-3%.

(SrO)

SrO is a component which can decrease the devitrification temperature ofa glass. SrO is not an essential component, but if SrO is comprised, thedevitrification resistance and meltability can be improved, andtherefore, SrO may be comprised. However, if the amount of SrO isexcessively large, the density increases. Therefore, if it is desirablethat the density be reduced, preferably substantially no SrO iscomprised. Therefore, in the glass substrate of this embodiment, the SrOcontent is preferably 0-10%, more preferably 0-8%. Note that, in orderto further reduce the weight, the SrO content is preferably less than3%, more preferably 2% or less, even more preferably 1% or less, andstill even more preferably 0.5% or less, and still even more preferably,substantially no SrO is comprised. In other words, the SrO content ispreferably 0% to less than 3% (no less than 0% and less than 3%), morepreferably 0-2%, even more preferably 0-1%, and still even morepreferably 0-0.5%, and still even more preferably, substantially no SrOis comprised. On the other hand, if it is desirable that the meltabilitybe improved, the SrO content is more preferably 1-8%, even morepreferably 3-8%.

(BaO)

BaO is a component which improves the devitrification resistance andmeltability. Also, if BaO is comprised, the coefficient of thermalexpansion increases and the density excessively increases. Therefore, inthe glass substrate of this embodiment, the BaO content is preferably0-10%, more preferably 0-5%, even more preferably 0-2%, and still evenmore preferably 0-1%. In view of the environmental load problem, morepreferably substantially no BaO is comprised.

(Li₂O, Na₂O)

Li₂O and Na₂O are components which improve the meltability of a glass,but increases the coefficient of thermal expansion of the glass, leadingto damage to a substrate in a heat treatment during production of adisplay, or significantly decreases the Tg and strain point of theglass, leading to an excessive decrease in the heat resistance.Therefore, in the glass substrate of this embodiment, the Li₂O and Na₂Ocontent is preferably 0-0.3%, more preferably 0-0.2%, and even morepreferably 0-0.1%, and still even more preferably, substantially no Li₂Oor Na₂O is comprised.

(K₂O)

K₂O is a component which increases the basicity of a glass to impartrefinability to the glass. K₂O is also a component which improves themeltability and decreases the specific resistance of a glass melt.Therefore, K₂O is not an essential component, but if K₂O is comprised,the specific resistance of a glass melt can be decreased and the claritycan be increased. However, if the amount of K₂O is excessively large,the coefficient of thermal expansion may increase, and the Tg and strainpoint may significantly decrease, leading to an excessive decrease inthe heat resistance. Therefore, in the glass substrate of thisembodiment, the K₂O content is preferably 0-0.8%, more preferably0.01-0.5%, and even more preferably 0.1-0.3%.

(ZrO₂, TiO₂)

ZrO₂ and TiO₂ are components which increase the chemical durability andthe Tg and strain point of a glass. ZrO₂ and TiO₂ are not essentialcomponents, but if ZrO₂ and TiO₂ are comprised, the Tg and strain pointcan be increased and the acid resistance can be improved. However, ifthe amounts of ZrO₂ and TiO₂ are excessively large, the devitrificationtemperature significantly increases, and therefore, the devitrificationresistance and the ease of forming may decrease. In particular, crystalsof ZrO₂ may precipitate in a cooling step, and these inclusions maycause a deterioration in the quality of the glass. TiO₂ is also acomponent which adds color to a glass, and therefore, is not suitablefor display substrates. For these reasons, in the glass substrate ofthis embodiment, the ZrO₂ and TiO₂ contents are each preferably 0-5%,more preferably 0-3%, even more preferably 0-2%, still even morepreferably 0-1%, and still even more preferably less than 0.5%. Stilleven more preferably, the glass substrate of this embodiment comprisessubstantially no ZrO₂ or TiO₂.

(ZnO)

ZnO is a component which improves the BHF resistance and meltability,and therefore, may be comprised, but is not an essential component.However, if the amount of ZnO is excessively large, the devitrificationtemperature may increase, the Tg and strain point may decrease, and thedensity may increase. Therefore, in the glass substrate of thisembodiment, the ZnO content is preferably 5% or less, more preferably 3%or less, even more preferably 2% or less, and still even more preferably1% or less. Still even more preferably, the glass substrate of thisembodiment comprises substantially no ZnO. In other words, the ZnOcontent is preferably 0-5%, more preferably 0-3%, even more preferably0-2%, and still even more preferably 0-1%.

Still even more preferably, the glass substrate of this embodimentcomprises substantially no ZnO.

(P₂O₅)

P₂O₅ is a component which decreases the melting temperature to improvethe meltability, and therefore, may be comprised, but is not anessential component. However, if the amount of P₂O₅ is excessivelylarge, P₂O₅ evaporates during melting of the glass, so that thenon-uniformity of the glass becomes significant, and therefore, a cordis likely to occur. Also, it is likely that the Tg and strain pointdecreases, the acid resistance significantly deteriorates, and the glassturns into milky white. Therefore, in the glass substrate of thisembodiment, the P₂O₅ content is preferably 3% or less, more preferably1% or less, and even more preferably 0.5% or less. Still even morepreferably, the glass substrate of this embodiment containssubstantially no P₂O₅. In other words, the P₂O₅ content is preferably0-3%, more preferably 0-1%, and even more preferably 0-0.5%. Still evenmore preferably, the glass substrate of this embodiment containssubstantially no P₂O₅.

(Refining Agent)

Any refining agent that has low environmental load and imparts excellentclarity to a glass may be employed, i.e., the present invention is notlimited to any particular refining agent. For example, the refiningagent may be at least one selected from the group consisting of metaloxides of Sn, Fe, Ce, Tb, Mo, and W. If the amount of the refining agentis excessively small, the foam quality deteriorates. Therefore, theamount of the refining agent added is, for example, within the range of0.01-1%, preferably 0.05-1%, more preferably 0.05-0.5%, even morepreferably 0.05-0.3%, and still even more preferably 0.05-0.2%, althoughit depends on the type of the refining agent or the composition of theglass. The refining agent is preferably SnO₂. However, SnO₂ is acomponent which decreases the devitrification resistance of a glass.Therefore, for example, if SnO₂ is used as the refining agent, the SnO₂content is preferably 0.01-0.3%, more preferably 0.03-0.2%, and evenmore preferably 0.05-0.15%.

(Fe₂O₃)

Fe₂O₃ is a component which works as a refining agent, and in addition,decreases the viscosity in a high-temperature region of a glass melt,and decreases the specific resistance. Fe₂O₃ is not an essentialcomponent, but is preferably comprised in a glass which has a highmelting temperature and is therefore difficult to melt in order todecrease the melting temperature and specific resistance. If the amountof Fe₂O₃ is excessively large, color may be added to the glass, so thatthe transmittance may decrease. Therefore, in the glass substrate ofthis embodiment, the Fe₂O₃ content is preferably 0-0.1%, more preferably0-0.08%, even more preferably 0.001-0.05%, and still even morepreferably 0.005-0.03%. Here, in a glass having a high meltingtemperature, the temperature of the melting step is high, the effect ofFe₂O₃ as a refining agent is likely to decrease. Therefore, if Fe₂O₃ isused singly as a refining agent, the clarity may decrease, so that thefoam quality of the glass substrate may deteriorate. Therefore, Fe₂O₃ ispreferably used in combination with SnO₂.

In the glass substrate of this embodiment, in view of the environmentalload problem, the Sb₂O₃ content is preferably 0-0.5%, more preferably0-0.3%, even more preferably 0-0.1%, and still even more preferably0-0.03%. Still even more preferably, the glass substrate of thisembodiment contains substantially no Sb₂O₃.

(Components Preferably Not Comprise)

In view of the environmental load problem, the glass substrate of thisembodiment contains substantially no As₂O₃, Sb₂O₃, PbO, or F.

Also, compound parameters of components comprised in the glass substrateof this embodiment will be described hereinafter.

((SiO₂+Al₂O₃)/(B₂O₃))

In the glass included in the glass substrate of this embodiment,(SiO₂+Al₂O₃)/(B₂O₃) is preferably 7.5-17, more preferably 8-17, and evenmore preferably 8.45-17.0. By satisfying the relationship, theaforementioned advantages are obtained. Note that when the glasscontains only less than 3% SrO+BaO in order to further reduce theweight, in order to reliably obtain the advantages (SiO₂+Al₂O₃)/(B₂O₃)is preferably 8.5-15.0, more preferably 9.5-14.0, even more preferably10.0-13.0, and still even more preferably 10.0-12.5. Moreover, in orderto prevent the increase of the devitrification temperature and achieve asufficient etching rate, (SiO₂+Al₂O₃)/(B₂O₃) is preferably 8-15, morepreferably 8-13, even more preferably 8-11, and still even morepreferably 8-10. On the other hand, when the glass contains 3% or moreSrO+BaO, (SiO₂+Al₂O₃)/(B₂O₃) is more preferably 9.5-17.0%, even morepreferably 10.0-17.0%.

(Alkaline-Earth Metal Oxides (RO: MgO+CaO+SrO+BaO))

RO is a component which improves the meltability. If the amount of RO isexcessively small, the meltability may deteriorate. However, if theamount of RO is excessively large, the Tg and strain point may decrease,the density may increase, the Young's modulus may decrease, and thecoefficient of thermal expansion may increase. Therefore, in the glassincluded in the glass substrate of this embodiment, the RO content ispreferably 3-25%, more preferably 4-20%. Note that when the glasscontains only less than 3% SrO+BaO in order to further reduce theweight, the RO content is more preferably no less than 5% and less than14%, even more preferably 6-14%, still even more preferably 8-13%, andstill even more preferably 9-12%. On the other hand, when the glasscontains 3% or more SrO+BaO, the RO content is more preferably no lessthan 5% and less than 18%, even more preferably 8-17%.

(CaO/RO)

When the glass contains only less than 3% SrO+BaO in order to furtherreduce the weight, CaO/RO is preferably 0.5 or more, more preferably 0.7or more, even more preferably more than 0.85, still even more preferably0.88 or more, still even more preferably 0.90 or more, still even morepreferably 0.92 or more, and still even more preferably 0.95 or more. Inother words, CaO/RO is preferably 0.5-1, more preferably 0.7-1, evenmore preferably more than 0.85 to 1, still even more preferably 0.88-1,still even more preferably 0.90-1, still even more preferably 0.92-1,and still even more preferably 0.95-1. If CaO/RO is within such a range,good devitrification resistance and meltability can be simultaneouslyobtained. Moreover, the density can be reduced. If only CaO is comprisedas a material, the Tg and strain point can be further increased thanwhen a plurality of alkaline-earth metal oxides are comprised. Note thateven if only CaO, which is an alkaline-earth metal oxide, is comprisedas a material, the obtained glass may contain another alkaline-earthmetal oxide as an impurity. If only CaO, which is an alkaline-earthmetal oxide, is comprised as a material, the value of CaO/RO of theobtained glass is, for example, about 0.98-1. CaO is also a preferablecomponent because a material for CaO is inexpensive and easilyavailable.

(SiO₂—(Al₂O₃/2))

If the value of SiO₂—(Al₂O₃/2) is excessively small, the etching ratemay increase, but the devitrification resistance may decrease. On theother hand, if the value is excessively large, the etching rate maydecrease. Therefore, in the glass included in the glass substrate ofthis embodiment, SiO₂—(Al₂O₃/2) is preferably 69 or less, morepreferably 50-68, even more preferably 55-65, still even more preferably57-63, and still even more preferably 58-62.

In order to perform etching (slimming) the glass substrate with a highproductivity, the etching rate is preferably 50 μm/h or more. On theother hand, if the etching rate is excessively high, a problem is likelyto occur in a reaction with a chemical solution in a panel productionstep. Therefore, for the glass included in the glass substrate, theetching rate is preferably 160 μm/h or less. The etching rate ispreferably 60-140 μm/h, more preferably 70-120 μm/h. In the presentinvention, the etching rate is defined as being measured under thefollowing conditions.

The etching rate (μm/h) is represented by the amount of a decrease inthe thickness of one surface of the glass substrate per unit time (onehour), where the glass substrate is immersed in an etchant (an acidmixture of HF (concentration: 1 mol/kg) and HCl (concentration: 5mol/kg)) at 40° C. for 1 hour.

(SiO₂+Al₂O₃)

If SiO₂+Al₂O₃ is excessively small, the Tg and strain point are likelyto decrease. On the other hand, if SiO₂+Al₂O₃ is excessively large, thedevitrification resistance is likely to deteriorate. Therefore, in theglass included in the glass substrate of this embodiment, SiO₂+Al₂O₃ ispreferably 70% or more, more preferably 75% or more, and even morepreferably 76-88%. Note that when the glass contains only less than 3%SrO+BaO in order to further reduce the weight, SiO₂+Al₂O₃ is morepreferably 78-88%, even more preferably 79-85%, and still even morepreferably 80-84%. Moreover, in order to prevent the increase of thedevitrification temperature, SiO₂+Al₂O₃ is more preferably 76-85%, evenmore preferably 76-83%, and still even more preferably 78-82%. On theother hand, when the glass contains 3% or more SrO+BaO, SiO₂+Al₂O₃ ismore preferably 76-86%, even more preferably 77-83%.

(Al₂O₃/SiO₂)

If Al₂O₃/SiO₂ exceeds 0.35, the devitrification resistance is likely todeteriorate. On the other hand, if Al₂O₃/SiO₂ is 0.05 or less, the Tgand strain point cannot be sufficiently increased. Therefore, in thisembodiment, Al₂O₃/SiO₂ is 0.05-0.35, preferably 0.07-0.30, and morepreferably 0.10-0.25.

(B₂O₃+P₂O₅)

If B₂O₃+P₂O₅ is excessively small, the meltability is likely todecrease. On the other hand, if B₂O₃+P₂O₅ is excessively large,B₂O₃+P₂O₅ evaporates during melting of the glass, so that thenon-uniformity of the glass becomes significant, and therefore, a cordis likely to occur. Moreover, the Tg and strain point are likely todecrease. Therefore, in the glass included in the glass substrate ofthis embodiment, B₂O₃+P₂O₅ is preferably 3-15%, more preferably 3-10%.Note that when the glass contains only less than 3% SrO+BaO in order tofurther reduce the weight, B₂O₃+P₂O₅ is more preferably no less than 3%and less than 9.5%, even more preferably no less than 4% and less than8.9%, still even more preferably 5-8.5%, and still even more preferably6-8%. Moreover, in order to improve the devitrification resistance,B₂O₃+P₂O₅ is more preferably 5-13%, even more preferably 5-12%, stilleven more preferably 6% to less than 10% (no less than 6% and less than10%). On the other hand, when the glass contains 3% or more SrO+BaO,B₂O₃+P₂O₅ is more preferably 3-9%, even more preferably 4-8%.

(CaO/B₂O₃)

Note that when the glass contains only less than 3% SrO+BaO in order tofurther reduce the weight, then if CaO/B₂O₃ is excessively low, the Tgand strain point are likely to decrease. On the other hand, if CaO/B₂O₃is excessively high, the meltability is likely to deteriorate.Therefore, in this embodiment, CaO/B₂O₃ is preferably 0.5 or more, morepreferably 0.7 or more, even more preferably 0.9 or more, still evenmore preferably more than 1.2, still even more preferably more than 1.2and no more than 5, still even more preferably more than 1.2 and no morethan 3, still even more preferably 1.3 or more and 2.5 or less, andstill even more preferably 1.3 or more and 2 or less. Moreover, in orderto improve the meltability, CaO/B₂O₃ is preferably 0.5-5, morepreferably 0.9-3, even more preferably more than 1 and no more than 2.5,still even more preferably more than 1 and no more than 2, still evenmore preferably more than 1.2 and no more than 2, and still even morepreferably more than 1.2 and no more than 1.5.

(SrO+BaO)

SrO and BaO are components which can decrease the devitrificationtemperature of a glass. These components are not essential, but if thesecomponents are comprised, the devitrification resistance and meltabilitycan be improved. However, if the amount of these components isexcessively large, the density increases.

Therefore, it is difficult to decrease the density and reduce theweight. Also, the coefficient of thermal expansion may increase.Therefore, in the glass included in the glass substrate of thisembodiment, SrO+BaO is preferably 10% or less. Note that, in order tofurther reduce the weight, SrO+BaO is more preferably 5% or less, evenmore preferably less than 3%, and still even more preferably less than2%. Still even more preferably, the glass included in the glasssubstrate of this embodiment contains substantially no SrO or BaO. Inother words, SrO+BaO is preferably 0-10%. In order to further reduce theweight, SrO+BaO is more preferably 0-5%, even more preferably 0% to lessthan 3% (no less than 0% and less than 3%), still even more preferably0% to less than 2% (no less than 0% and less than 2%), still even morepreferably 0% to less than 1% (no less than 0% and less than 1%), andstill even more preferably 0% to less than 0.5% (no less than 0% andless than 0.5%). Still even more preferably, the glass included in theglass substrate of this embodiment contains no SrO or BaO.

(RO+ZnO+B₂O₃)

If RO+ZnO+B₂O₃ is excessively small, the viscosity in a high-temperatureregion is likely to be high, and the clarity and glass meltability arelikely to decrease. On the other hand, if RO+ZnO+B₂O₃ is excessivelylarge, the Tg and strain point are likely to decrease. Therefore, in theglass included in the glass substrate of this embodiment, RO+ZnO+B₂O₃ ispreferably 7-30%, more preferably 10-27%. Note that when the glasscontains only less than 3% SrO+BaO in order to further reduce theweight, RO+ZnO+B₂O₃ is more preferably 12-22%, even more preferably14-21%, and still even more preferably 16-20%. Moreover, in order toimprove the meltability, RO+ZnO+B₂O₃ is more preferably 12-27%, evenmore preferably 14-25%, and still even more preferably 17-23%. On theother hand, when the glass contains 3% or more SrO+BaO, RO+ZnO+B₂O₃ ismore preferably 13-27%, even more preferably 15-25%.

(Alkali Metal Oxide (R₂O: Li₂O+Na₂O+K₂O))

R₂O is a component which increases the basicity of a glass to facilitateoxidation of a refining agent, thereby imparting clarity to the glass.R₂O is also a component which facilitates improvement of the meltabilityof a glass and decrease of the specific resistance of the glass, and maybe comprised. R₂O is not an essential component, but if it is comprised,can decrease the specific resistance and improve the clarity andmeltability. However, if the amount of R₂O is excessively large, the Tgand strain point may excessively decrease, and the coefficient ofthermal expansion may increase. Therefore, in the glass included in theglass substrate of this embodiment, R₂O is preferably 0-0.8%, morepreferably 0.01-0.5%, and even more preferably 0.1-0.3%.

(K₂O/R₂O)

K₂O has a larger molecular weight than those of Li₂O and Na₂O, andtherefore, runs off the glass substrate to a lesser extent. Therefore,if R₂O is comprised, K₂O is preferably comprised at a higher ratio. K₂Ois preferably comprised at a higher ratio than that of Li₂O (K₂O>Li₂O issatisfied). K₂O is preferably comprised at a higher ratio than that ofNa₂O (K₂O>Na₂O is satisfied). K₂O/R₂O is preferably 0.5 or more, morepreferably 0.6 or more, even more preferably 0.7 or more, still evenmore preferably 0.8 or more, and still even more preferably 0.95 ormore. In other words, K₂O/R₂O is preferably 0.5-1, more preferably0.6-1, even more preferably 0.7-1, still even more preferably 0.8-1, andstill even more preferably 0.95-1.

The glass included in the glass substrate of this embodiment can beobtained by appropriately combining the above components. Thecombination of the components is not limited. Example combinations willbe described hereinafter. The glass may contain

65-78% SiO₂

3-20% Al₂O₃

3-15% B₂O₃

0% to less than 2% (no less than 0% and less than 2%) MgO

3.6-16% CaO

0-2% SrO

0% to less than 1% (no less than 0% and less than 1%) BaO

where

the B₂O₃, P₂O₅, and CaO contents in mol % may satisfy relationshipsB₂O₃+P₂O₅=3-15% and CaO/B₂O₃>1.2.

Alternatively, the glass may contain

65-78% SiO₂

3-20% Al₂O₃

3-9.5% B₂O₃

0% to less than 2% (no less than 0% and less than 2%) MgO

3.6-16% CaO

0-2% SrO

substantially no BaO

where

the B₂O₃, P₂O₅, and CaO contents in mol % may satisfy relationshipsB₂O₃+P₂O₅=3-9.5% and CaO/B₂O₃>1.2.

The glass substrate of this embodiment is a substrate for displays.Specifically, the glass substrate of this embodiment is suitable as aflat panel display glass substrate on which the p-Si TFT is formed. Theglass substrate of this embodiment is also suitable as a liquid crystaldisplay glass substrate and an organic EL display glass substrate. Inparticular, the glass substrate of this embodiment is suitable as a p-SiTFT liquid crystal display glass substrate and organic EL display glasssubstrate. The glass substrate of this embodiment is suitable as adisplay glass substrate for mobile terminals for which a high resolutionis required, among other things. Alternatively, the glass substrate ofthis embodiment is suitable as an oxide semiconductor thin film flatpanel display glass substrate. More specifically, the glass substrate ofthis embodiment is suitable as a glass substrate used in a flat paneldisplay which is produced by forming an oxide semiconductor thin filmTFT on a substrate surface.

The size of the glass substrate of this embodiment can be appropriatelyadjusted, depending on the size of a display to which the glasssubstrate is applied, and therefore, is not particularly limited. Thelength in the width direction of the glass substrate is, for example,500-3500 mm, preferably 1000-3500 mm, and more preferably 2000-3500 mm.The length in the longitudinal direction of the glass substrate, forexample, 500-3500 mm, preferably 1000-3500 mm, and more preferably2000-3500 mm. As the size of the glass substrate increases, theproductivity of liquid crystal displays or organic EL displays isimproved.

The thickness of the glass substrate of this embodiment can beappropriately adjusted, depending on the size of a display to which theglass substrate is applied, and therefore, is not particularly limited.However, if the glass substrate is excessively thin, the strength of theglass substrate itself decreases. For example, damage is likely to occurduring production of a liquid crystal display. On the other hand, if theglass substrate is excessively thick, the glass substrate is notsuitable for a display which is desired to be thinner. Also, if theglass substrate is excessively thick, the glass substrate has a heavyweight, and therefore, it is difficult to reduce the weight of a liquidcrystal display. Therefore, the thickness of the glass substrate of thisembodiment is preferably 0.1-1.1 mm, more preferably 0.1-0.7 mm, evenmore preferably 0.3-0.7 mm, and still even more preferably 0.3-0.5 mm.

The glass substrate of this embodiment is manufactured by a methodincluding a melting step of melting a glass material to produce moltenglass, a forming step of forming the molten glass into a glass plate,and an annealing step of annealing the glass plate. Note that the ratioof heat shrinkage of the glass plate is 75 ppm or less, preferably 60ppm or less. The glass included in the glass substrate has adevitrification temperature of 1250° C. or less, and contains, asexpressed in mol %, SiO₂ (55-80%), Al₂O₃ (3-20%), B₂O₃ (3-15%), RO(3-25%: the total amount of MgO, CaO, SrO, and BaO) as a glasscomposition. The SiO₂, Al₂O₃, and B₂O₃ contents in mol % satisfy arelationship (SiO₂+Al₂O₃)/(B₂O₃)=7.5-17, preferably 8.45-17.0. In thiscase, the glass preferably has a strain point of 665° C. or more.

The glass substrate of this embodiment can be manufactured by a knownmethod for manufacturing a glass substrate. Also, a known forming methodcan be used, and a float process or a downdraw process is preferable. Inparticular, the overflow downdraw process is preferable. The glasssubstrate formed by the glass substrate formed by the downdraw processhas main surfaces which are made by hot forming by hot forming, andtherefore, is considerably highly flat and smooth. Therefore, it is nolonger necessary to polish the surface of the glass substrate after theforming, resulting in a reduction in manufacturing cost and animprovement in productivity. Moreover, both main surfaces of the glasssubstrate formed by the downdraw process have a uniform composition, andtherefore, can be uniformly etched during an etching process. Inaddition, by forming by the downdraw process, the glass substrate canobtain a surface condition free from a microcrack. As a result, thestrength of the glass substrate itself can be improved.

In order to manufacture the glass substrate having a heat shrinkageratio of 75 ppm or less, preferably 60 ppm or less, it is desirable thatconditions under which annealing is performed be adjusted asappropriate. For example, when the downdraw process is used, annealingis desirably performed while keeping the temperature of the glass platewithin the temperature range of Tg° C. to Tg−100° C. for 20-120 sec. Inother words, when the downdraw process is used, annealing is desirablyperformed so that the glass plate is cooled to the temperature range ofTg° C. to Tg−100° C. in 20-120 sec. If the time is less than 20 sec, theamount of heat shrinkage may not be sufficiently reduced. On the otherhand, if the time exceeds 120 sec, the productivity decreases and thesize of the glass manufacturing equipment (annealing furnace) increases.Therefore, in order to reduce the ratio of heat shrinkage while keepingthe cost and productivity, annealing is preferably performed whilekeeping the temperature of the glass plate within the temperature rangeof Tg° C. to Tg−100° C. for 20-120 sec, more preferably 30-120 sec, andeven more preferably 50-100 sec. In other words, annealing is preferablyperformed so that the glass plate is cooled to the temperature range ofTg° C. to Tg−100° C. in 20-120 sec, more preferably 30-120 sec, and evenmore preferably 50-100 sec. Alternatively, annealing is preferablyperformed so that the average rate of cooling a center portion of theglass plate within the temperature range of ° C. to Tg−100° C. is50-300° C./min. If the average cooling rate exceeds 300° C./min, theamount of heat shrinkage may not be sufficiently reduced. On the otherhand, if the average cooling rate is less than 50° C./min, theproductivity decreases and the size of the glass manufacturing equipment(annealing furnace) increases. Therefore, the average cooling rate rangefor reducing the ratio of heat shrinkage while keeping the cost andproductivity is preferably 50-300° C./min, more preferably 50-200°C./min, and even more preferably 60-120° C./min. On the other hand, byseparately providing a heat shrinkage reduction treatment (off-lineannealing) step after the annealing step, the ratio of heat shrinkagecan be reduced. However, if the off-line annealing step is providedseparately from the annealing step, the productivity decreases and thecost increases. Therefore, as described above, the heat shrinkagereduction treatment (off-line annealing) of controlling the rate ofcooling the glass plate is more preferably performed in the annealingstep so that the ratio of heat shrinkage falls within the predeterminedrange.

The water content of glass may be represented by a β-OH value. As theβ-OH value decreases, the Tg and strain point tend to increase. On theother hand, as the β-OH value increases, the melting temperature tendsto decrease. In order to simultaneously achieve both the increase of theTg and strain point and the improvement of the meltability, the β-OHvalue is preferably 0.05-0.40 mm⁻¹, more preferably 0.10-0.35 mm⁻¹, evenmore preferably 0.10-0.30 mm⁻¹, and still even more preferably 0.10-0.25mm⁻¹. The β-OH value can be adjusted by selecting the material.

For example, the β-OH value can be increased and decreased by selectinga material having a high water content (e.g., a hydroxide material) oradjusting the content of a material (e.g., a chloride) which reduces thewater content of a glass. The β-OH value can also be adjusted byadjusting the ratio of gas burning heating (oxygen burning heating) andelectrical heating (direct electrical heating) for melting glass. Theβ-OH value can also be increased by increasing the amount of moisture infurnace atmosphere or bubbling water vapor with respect to molten glassduring the melting. Note that the β-OH value of a glass is calculatedbased on the infrared absorption spectrum of the glass by the followingexpression:β-OH value=(1/X)log 10(T1/T2)

X: glass thickness (mm)

T1: transmittance (%) at a reference wavelength of 2600 nm

T2: minimum transmittance (%) in the vicinity of a hydroxyl groupabsorption wavelength of 2800 nm

As examples of the flat panel display glass substrate of this embodimentobtained from the present disclosure, first to fourth glass substrateswill be described hereinafter. As examples of the method formanufacturing the glass substrate of this embodiment obtained from thepresent disclosure, first to fourth manufacturing methods will bedescribed hereinafter.

The first flat panel display glass substrate includes a glasscomprising, as expressed in mol %:

55-80% SiO₂;

3-20% Al₂O₃;

3-15% B₂O₃; and

3-25% RO (the total amount of MgO, CaO, SrO, and BaO)

wherein

in the glass the contents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfy arelationship (SiO₂+Al₂O₃)/(B₂O₃)=7.5-17,

the strain point of the glass is 665° C. or more, and

the devitrification temperature of the glass is 1250° C. or less, and

the ratio of heat shrinkage of the glass substrate is 75 ppm or less.

The second flat panel display glass substrate includes a glasscomprising, as expressed in mol %:

55-80% SiO₂;

3-20% Al₂O₃;

3-15% B₂O₃; and

RO (the total amount of MgO, CaO, SrO, and BaO) 3-25%

wherein

in the glass the contents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfy arelationship (SiO₂+Al₂O₃)/(B₂O₃)=8.45-17.0, and

the devitrification temperature of the glass is 1250° C. or less, and

the ratio of heat shrinkage of the glass substrate is 60 ppm or less.

The third flat panel display glass substrate includes a glasscomprising, as expressed in mol %,

65-78% SiO₂

3-20% Al₂O₃

3-15% B₂O₃

0% to less than 2% MgO

3.6-16% CaO

0-2% SrO

0% to less than 1% BaO

where

the contents in mol % of B₂O₃, P₂O₅, and CaO satisfy relationshipsB₂O₃+P₂O₅=3-15% and CaO/B₂O₃>1.2,

the strain point of the glass is 665° C. or more, and

the devitrification temperature of the glass is 1250° C. or less.

The fourth flat panel display glass substrate includes a glasscomprising, as expressed in mol %,

65-78% SiO₂

3-20% Al₂O₃

3-9.5% B₂O₃

0% to less than 2% MgO

3.6-16% CaO

0-2% SrO

substantially no BaO

where

the contents in mol % of B₂O₃, P₂O₅, and CaO satisfy relationshipsB₂O₃+P₂O₅=3-9.5% and CaO/B₂O₃>1.2, and

the devitrification temperature of the glass is 1250° C. or less.

The first to fourth flat panel display glass substrates are suitable asflat panel display glass substrates on which the p-Si TFT is formed. Inparticular, the first to fourth flat panel display glass substrates aresuitable as liquid crystal display glass substrates on which the p-SiTFT is formed. Alternatively, the first to fourth flat panel displayglass substrates are also suitable as organic EL display glasssubstrates. Alternatively, the first to fourth flat panel display glasssubstrates are suitable as display glass substrates on which an oxidesemiconductor thin film transistor is formed.

The first method for manufacturing a flat panel display glass substrateincludes

a melting step of melting a glass material for a glass comprising, asexpressed in mol %, 55-80% SiO₂, 3-20% Al₂O₃, 3-15% B₂O₃, and 3-25% RO(the total amount of MgO, CaO, SrO, and BaO), with the contents in mol %of SiO₂, Al₂O₃, and B₂O₃ satisfying a relationship(SiO₂+Al₂O₃)/(SiO₂O₃)=7.5-17.0, the strain point of the glass being 665°C. or more, and the devitrification temperature of the glass being 1250°C. or less, to produce a molten glass,

a forming step of forming the molten glass into a glass plate, and

an annealing step of annealing the glass plate,

where

the rate of heat shrinkage of the glass plate is 75 ppm or less.

The second method for manufacturing a flat panel display glass substrateincludes a melting step of melting a glass material for a glasscomprising, as expressed in mol %, 55-80% SiO₂, 3-20% Al₂O₃, 3-15% B₂O₃,and 3-25% RO (the total amount of MgO, CaO, SrO, and BaO), with thecontents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfying a relationship(SiO₂+Al₂O₃)/(SiO₂O₃)=8.45-17.0 and the devitrification temperature ofthe glass being 1250° C. or less, to produce a molten glass,

a forming step of forming the molten glass into a glass plate, and

an annealing step of annealing the glass plate,

where

the rate of heat shrinkage of the glass plate is 60 ppm or less.

The third method for manufacturing a flat panel display glass substrateincludes

a melting step of melting a glass material for a glass comprising, asexpressed in mol %, 65-78% SiO₂, 3-20% Al₂O₃, 3-15% B₂O₃, 0% to lessthan 2% MgO, 3.6-16% CaO, 0-2% SrO, and 0% to less than 1% BaO, with thecontents in mol % of B₂O₃, P₂O₃, and CaO satisfying relationshipsB₂O₃+P₂O₅=3-15% and CaO/B₂O₃>1.2, the strain point of the glass being665° C. or more, and the devitrification temperature of the glass being1250° C. or less, to produce a molten glass,

a forming step of forming the molten glass into a glass plate, and

an annealing step of annealing the glass plate.

The fourth method for manufacturing a flat panel display glass substrateincludes

a melting step of melting a glass material for a glass comprising, asexpressed in mol %, 65-78% SiO₂, 3-20% Al₂O₃, 3-9.5% B₂O₃, 0% to lessthan 2% MgO, 3.6-16% CaO, 0-2% SrO, and substantially no BaO, with thecontents in mol % of B₂O₃, P₂O₃, and CaO satisfying relationshipsB₂O₃+P₂O₅=3-9.5% and CaO/B₂O₃>1.2 and the devitrification temperature ofthe glass being 1250° C. or less, to produce a molten glass,

a forming step of forming the molten glass into a glass plate, and

an annealing step of annealing the glass plate.

In the annealing steps of the first to fourth manufacturing methods ofthe flat panel display glass substrate, a heat shrinkage reductiontreatment for reducing the rate of heat shrinkage is preferablyperformed by controlling the rate of cooling the glass plate. Also, inthe annealing steps, the heat shrinkage reduction treatment is morepreferably performed so that the average cooling rate of a centerportion of the glass plate within the temperature range of Tg° C. toTg−100° C. is 50-300° C./min.

EXAMPLES

Next, the glass substrate of the present invention will be described indetail by way of example. Note that the present invention is notintended to be limited to examples described below.

<First Glass Substrate>

The first glass substrate will be described by way of example. Note thatthe first glass substrate includes a glass comprising, as expressed inmol %:

55-80% SiO₂;

3-20% Al₂O₃;

3-15% B₂O₃; and

3-25% RO (the total amount of MgO, CaO, SrO, and BaO)

wherein

in the glass the contents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfy arelationship (SiO₂+Al₂O₃)/(B₂O₃)=7.5-17,

the strain point of the glass is 665° C. or more, and

the devitrification temperature of the glass is 1250° C. or less, and

the rate of heat shrinkage of the glass substrate is 75 ppm or less.

Examples 1-1 to 1-24 and Comparative Examples 1-1 to 1-6

Sample glasses of Examples 1-1 to 1-24 and Comparative Examples 1-1 to1-6 were produced by a procedure described below so that the sampleglasses have glass compositions shown in Tables 1-1 and 1-2. For theobtained sample glasses and sample glass substrates, devitrificationtemperature, Tg, average coefficient of thermal expansion within therange of 100-300° C., rate of heat shrinkage, density, strain point,melting temperature (glass temperature where viscosity is 10^(2.5)dPa·s), liquidus viscosity, and specific resistance at 1550° C., weremeasured.

(Production of Sample Glass)

Initially, glass material batches (hereinafter referred to as “batches”)having glass compositions shown in Tables 1-1 and 1-2 were preparedusing typical glass materials, i.e., silica, alumina, boron oxide,potassium carbonate, basic magnesium carbonate, calcium carbonate,strontium carbonate, tin dioxide, and iron(III) oxide, in amounts whichwould provide 400 g of a glass.

The prepared batch was melted, followed by refining, in a platinumcrucible. Initially, the crucible was held for 4 hours in an electricalfurnace which was set to 1575° C. to melt the batch. Next, thetemperature of the electrical furnace was increased to 1640° C., and theplatinum crucible was held for 2 hours to perform refining on the glassmelt. Thereafter, the glass melt was poured onto an iron plate outsidethe furnace, and was cooled and solidified to obtain a glass piece.Following this, an annealing process was performed on the glass piece.In the annealing process, the glass piece was held for 2 hours inanother electrical furnace which was set to 800° C., and thereafter,cooled for 2 hours until the temperature dropped to 740° C., and furthercooled for 2 hours until the temperature dropped to 660° C. Thereafter,the electrical furnace was turned off, and the glass piece was cooled toroom temperature. The glass piece after the annealing process was asample glass. The sample glass was used to measure properties(devitrification temperature, melting temperature, specific resistance,density, coefficient of thermal expansion, and Tg and strain point),which are not affected by annealing conditions and/or cannot be measuredin the form of a substrate.

The sample glass was cut, ground, and polished to produce a sample glasssubstrate of 30 mm×40 mm×0.7 mm whose top and bottom surfaces are amirror surface. The sample glass substrate was used to measure β-OH,which is not affected by annealing conditions.

Moreover, the sample glass substrate was formed into a rectangularparallelepiped having a width of 5 mm and a length of 20 mm by acommonly used glass processing technique. The resulting sample glasssubstrate was kept at Tg for 30 min, and thereafter, cooled at a rate of100° C./min until the temperature reached Tg−100° C. and then cooleduntil the temperature reached room temperature. The sample glasssubstrate for measurement of heat shrinkage was thus prepared.

(Method for Measuring Devitrification Temperature)

The sample glass was pulverized, and was passed through a 2380-μm sieve.Glass particles which were retained on a 1000-μm sieve were obtained.The glass particles were immersed in ethanol, followed by ultrasoniccleaning and then drying in a constant temperature bath. Twenty-fivegrams of the dried glass particles were placed to substantially auniform thickness in a platinum boat having a width of 12 mm, a lengthof 200 mm, and a depth of 10 mm. The platinum boat was held for 5 hoursin an electrical furnace having a temperature gradient of 1080-1320° C.(for Examples 1-1 to 1-6, 1-8 to 1-24 and Comparative Examples 1-1 and1-3 to 1-5) or 1140-1380° C. (for Examples 1-7 and Comparative Examples1-2 and 1-6). Thereafter, the platinum boat was removed from thefurnace. Devitrification occurring inside the glass was observed by a50× optical microscope. A highest temperature at which devitrificationwas observed was defined as a devitrification temperature.

(Melting Temperature)

The melting temperature of the sample glass was measured using aplatinum sphere dragging type automatic viscometer. A temperature atwhich the viscosity was 10^(2.5) dPa·s was calculated from themeasurement result, and was defined as the melting temperature.

(Liquidus Viscosity)

A viscosity at the devitrification temperature was calculated from themeasurement result of the melting temperature, and was defined as aliquidus viscosity.

(Specific Resistance)

The specific resistance of the sample glass as it is melted was measuredby four-terminal sensing using the 4192A LF impedance analyzer(manufactured by HP). The specific resistance value at 1550° C. wascalculated from the measurement result.

(Method for Measuring Average Coefficient of Thermal Expansion and Tgwithin Range of 100-300° C.)

The sample glass was processed into the form of a cylinder having adiameter (φ) of 5 mm and a length of 20 mm, and was used as a testpiece. The temperature and the amount of expansion/shrinkage of the testpiece were measured in the process of increasing the temperature of thetest piece using a differential thermal dilatometer (Thermo Plus2TMA8310). In this case, the rate of increasing the temperature was 5°C./min. The average coefficient of thermal expansion and the Tg withinthe temperature range of 100-300° C. were measured based on themeasurement results of the temperature and the amount ofexpansion/shrinkage of the test piece. Note that the Tg as used hereinrefers to a value of a sample glass which was measured by holding aglass piece in another electrical furnace which was set to 800° C. for 2hours, cooling the glass piece for 2 hours until the temperature droppedto 740° C., and then cooling the glass piece for 2 hours until thetemperature dropped to 660° C., and thereafter, turning off theelectrical furnace, and cooling the glass piece until the temperaturedropped to room temperature.

(Strain Point)

The sample glass was cut and ground into the form of a prism having a3-mm square base and a length of 55 mm, and was used as a test piece.The test piece was measured using a beam bending measurement device(manufactured by TokyoKogyo Co., Ltd.). The strain point was calculatedby a beam bending technique (ASTM C-598).

(Density)

The sample glass was mirror-polished to produce a plate-like sample of5×30×30 mm. This sample was used to measure the density of the glassusing Archimedes' technique.

(Rate of Heat Shrinkage)

The rate of heat shrinkage was calculated from the amount of shrinkageof the glass substrate for measurement of heat shrinkage after a heattreatment at 550° C. for 2 hours using the following expression:the rate of heat shrinkage (ppm)={the amount of shrinkage of the glasssubstrate after the heat treatment/the length of the glass substratebefore the heat treatment}×10⁶

In this example, the amount of shrinkage was specifically measured bythe following technique.

The heat shrinkage sample glass was heated from room temperature to 550°C. using a differential thermal dilatometer (Thermoflex TMA8140manufactured by Rigaku Corporation), was held for 2 hours, and wascooled to room temperature. The amount of shrinkage of the sample glassbetween before and after the heat treatment was measured. In this case,the rate of increasing the temperature was 10° C./min.

(Etching Rate)

The glass substrate was immersed in an etchant (an acid mixture of HF(concentration: 1 mol/kg) and HCl (concentration: 5 mol/kg)) at 40° C.for 1 hour. Thereafter, a reduction (μm) in the thickness of one surfaceof the glass substrate was measured. The reduction (μm) per unit time(one hour) was defined as an etching rate (μm/h).

TABLE 1-1 Examples 1-1 1-2 1-3 1-4 1-5 1-6 1-7 Composition SiO₂ 71.771.6 70.8 70.5 70.5 70.3 69.4 (mol %) B₂O₃ 6.0 6.0 6.9 7.4 7.4 7.8 8.7Al₂O₃ 11.1 11.1 11.0 10.9 10.9 10.9 10.8 K₂O 0.17 0.17 0.17 0.17 0.40MgO 1.0 CaO 11.1 11.1 11.0 10.9 9.9 10.9 9.8 SrO 0.8 BaO SnO₂ 0.08 0.080.08 0.08 0.08 0.08 0.08 Fe₂O₃ 0.022 0.022 0.022 0.022 (SiO₂ +Al₂O₃)/B₂O₃ 13.8 13.8 11.8 11.0 11.0 10.3 9.2 SiO₂ + Al₂O₃ 82.8 82.681.8 81.4 81.4 81.2 80.2 RO + B₂O₃ + ZnO 17.1 17.1 17.9 18.3 18.3 18.719.3 Al₂O₃/SiO₂ 0.15 0.15 0.15 0.15 0.15 0.15 0.15 RO 11.1 11.1 11.010.9 10.9 10.9 10.6 B₂O₃ + P₂O₅ 6.0 6.0 6.9 7.4 7.4 7.8 8.7 CaO/RO 1 1 11 0.91 1 0.93 SiO₂—Al₂O₃/2 66.1 66.0 65.4 65.0 65.0 64.8 64.1 β-OH 0.110.12 0.11 0.11 0.12 0.13 0.13 Properties devitrification temperature1233 1230 1213 1189 1206 1187 <1140 (° C.) Tg (° C.) 782 776 766 758 751761 741 average coefficient of thermal 34.2 34.0 32.9 32.6 33.1 33.236.3 expansion (×10⁻⁷) (100-300° C.) rate of heat shrinkage (ppm) 31 3644 48 52 46 40 density (g/cm³) 2.41 2.41 2.40 2.39 2.39 2.38 2.40 strainpoint (° C.) 723 716 707 709 704 707 685 melting temperature (° C.) 16441632 1620 1608 1609 1610 1644 liquidus viscosity (log η) 5.0 5.0 5.1 5.25.0 5.2 5.3 specific resistance (Ω · cm) 243 193 194 195 194 248 170(1550° C.) etching rate (μm/h) 65 65 67 69 69 69 72 Examples 1-8 1-91-10 1-11 1-12 1-13 1-14 1-15 Composition SiO₂ 69.7 67.2 66.7 69.7 67.567.3 67.8 66.9 (mol %) B₂O₃ 9.7 4.7 5.0 5.0 7.5 8.3 7.8 9.2 Al₂O₃ 10.812.5 13.2 12.2 12.9 12.7 12.5 12.2 K₂O 0.17 0.17 0.17 0.20 0.17 0.170.17 MgO 6.9 7.4 5.8 CaO 8.9 1.7 1.3 1.42 11.7 11.5 11.5 11.4 SrO 0.86.8 6.2 5.7 BaO SnO₂ 0.08 0.09 0.09 0.09 0.10 0.08 0.08 0.08 Fe₂O₃ 0.020.02 0.02 0.02 (SiO₂ + Al₂O₃)/B₂O₃ 8.3 17.0 16.0 16.4 10.7 9.7 10.3 8.6SiO₂ + Al₂O₃ 80.5 79.7 79.9 81.9 80.4 80.0 80.4 79.2 RO + B₂O₃ + ZnO19.4 20.1 19.9 17.9 19.2 19.8 19.4 20.5 Al₂O₃/SiO₂ 0.15 0.19 0.20 0.180.19 0.19 0.18 0.18 RO 9.7 15.4 14.9 12.9 11.7 11.5 11.5 11.4 B₂O₃ +P₂O₅ 9.7 4.7 5.0 5.0 7.5 8.3 7.8 9.2 CaO/RO 0.92 0.11 0.09 0.11 1 1 1 1SiO₂—Al₂O₃/2 64.3 61.0 60.1 63.6 61.1 61.0 61.6 60.8 β-OH 0.11 0.13 0.130.14 0.12 0.11 0.11 0.10 Properties devitrification temperature 11511241 1219 1215 1230 1220 1236 1193 (° C.) Tg (° C.) 745 749 764 768 763754 760 741 average coefficient of thermal 29.6 39.8 36.4 33.6 36.0 35.936.0 36.1 expansion (×10⁻⁷) (100-300° C.) rate of heat shrinkage (ppm)32 42 29 27 28 33 31 40 density (g/cm³) 2.37 2.58 2.55 2.52 2.40 2.412.42 2.40 strain point (° C.) 695 694 712 711 712 702 710 695 meltingtemperature (° C.) 1650 1532 1538 1553 1587 1582 1579 1567 liquidusviscosity (log η) 5.5 4.3 4.5 4.7 4.6 4.7 4.6 4.9 specific resistance (Ω· cm) 253 203 203 236 137 133 129 142 (1550° C.) etching rate (μm/h) 7183 85 73 80 82 80 83

TABLE 1-2 Examples 1-16 1-17 1-18 1-19 1-20 1-21 1-22 1-23 CompositionSiO₂ 67.64 72.0 66.5 66.5 66.5 63.5 70.5 70.5 (mol %) B₂O₃ 7.83 6.4 9.59.5 4.5 4.5 7.4 7.4 Al₂O₃ 12.73 11.4 11.4 12.4 10.4 10.4 10.9 10.9 K₂O0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 MgO 2.0 CaO 6.5 9.9 12.3 11.318.3 21.3 8.9 9.9 SrO 5 1.0 BaO SnO₂ 0.08 0.08 0.08 0.08 0.08 0.08 0.080.08 Fe₂O₃ 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 (SiO₂ +Al₂O₃)/B₂O₃ 10.3 13.1 8.2 8.3 16.9 16.2 11.0 11.0 SiO₂ + Al₂O₃ 80.4 83.477.9 78.9 76.9 73.9 81.4 81.4 RO + B₂O₃ + ZnO 19.4 16.3 21.8 20.8 22.825.8 18.3 18.3 Al₂O₃/SiO₂ 0.19 0.16 0.17 0.19 0.16 0.16 0.15 0.15 RO11.5 9.9 12.3 11.3 18.3 21.3 10.9 10.9 B₂O₃ + P₂O₅ 7.83 6.4 9.5 9.5 4.54.5 7.4 7.4 CaO/RO 0.57 1 1 1 1 1 0.82 0.91 SiO₂—Al₂O₃/2 61.3 66.3 60.760.2 61.2 58.2 65.0 65.0 β-OH 0.12 0.12 0.11 0.11 0.10 0.10 0.12 0.12Properties devitrification temperature 1221 1235 1196 1208 1228 12061201 1207 (° C.) Tg (° C.) 758 781 731 743 739 732 742 752 averagecoefficient of 38.2 33.3 37.2 36 46.8 50.9 30.4 35.0 thermal expansion(×10⁻⁷) (100-300° C.) rate of heat shrinkage 33 23 47 39 49 54 39 34(ppm) density (g/cm³) 2.48 2.38 2.40 2.40 2.50 2.55 2.38 2.41 strainpoint (° C.) 703 731 681 693 689 682 695 702 melting temperature (° C.)1595 1640 1554 1560 1548 1541 1614 1610 liquidus viscosity (log η) 4.84.9 4.7 4.6 4.3 4.4 5.1 5.0 specific resistance (Ω · cm) 138 207 179 191108 73 193 196 (1550° C.) etching rate (μm/h) 83 64 83 85 81 92 69 69Examples Comparative Examples 1-24 1-1 1-2 1-3 1-4 1-5 1-6 CompositionSiO₂ 70.5 71.7 71.7 66.4 67.64 67.64 67.64 (mol %) B₂O₃ 7.4 4.0 11.07.83 7.83 7.83 Al₂O₃ 10.9 11.1 11.1 10.9 12.73 12.73 12.73 K₂O 0.17 0.180.17 0.17 0.17 MgO 2.8 1 3 5 CaO 8.9 13.1 17.1 6.8 10.5 8.5 6.5 SrO 2.01.69 BaO SnO₂ 0.08 0.08 0.09 0.09 0.08 0.08 0.08 Fe₂O₃ 0.022 0.03 0.0220.022 0.022 (SiO₂ + Al₂O₃)/B₂O₃ 11.0 20.7 7.0 10.3 10.3 10.3 SiO₂ +Al₂O₃ 81.4 82.8 82.8 77.4 80.4 80.4 80.4 RO + B₂O₃ + ZnO 18.3 17.1 17.122.3 19.4 19.4 19.4 Al₂O₃/SiO₂ 0.15 0.15 0.15 0.16 0.19 0.19 0.19 RO10.9 13.1 17.1 11.3 11.5 11.5 11.5 B₂O₃ + P₂O₅ 7.4 4.0 11.0 7.83 7.837.83 CaO/RO 0.82 1 1 0.60 0.91 0.74 0.57 SiO₂—Al₂O₃/2 65.0 66.1 66.161.0 61.3 61.3 61.3 β-OH 0.12 0.13 0.11 0.11 0.11 0.11 0.12 Propertiesdevitrification temperature 1200 1282 1330 1196 1260 1294 1324 (° C.) Tg(° C.) 753 786 826 707 758 749 746 average coefficient of 35.8 29.8 41.034.3 34.4 33.3 32.8 thermal expansion (×10⁻⁷) (100-300° C.) rate of heatshrinkage 33 17 13 114 32 37 38 (ppm) density (g/cm³) 2.42 2.445 2.5102.40 2.41 2.40 2.40 strain point (° C.) 703 725 774 660 708 697 691melting temperature (° C.) 1608 1675 1701 1529 1585 1580 1577 liquidusviscosity (log η) 5.1 4.7 4.4 4.6 4.4 4.2 4.0 specific resistance (Ω ·cm) 197 230 188 165 132 130 128 (1550° C.) etching rate (μm/h) 69 65 6582 83 81 79

The glass substrates of Examples 1-1 to 1-24 had a Tg of 720° C. ormore, and the rate of heat shrinkage and devitrification temperaturethereof satisfied the conditions of the first glass substrate of thepresent invention. The glasses of Examples 1-1 to 1-24 had a meltingtemperature of 1680° C. or less, i.e., good meltability. Therefore, theglass substrates of Examples 1-1 to 1-24 have excellent properties andcan be used in displays to which the p-Si TFT is applied. On the otherhand, the ratios of heat shrinkage or devitrification temperatures ofthe glasses of Comparative Examples 1-1 to 1-6 did not satisfy theconditions of the first glass substrate of the present invention. Themelting temperature of the glass of Comparative Example 2 exceeded 1680°C., i.e., good meltability was not obtained. Thus, the glass substratesof Comparative Examples 1-1 to 1-6 were not suitable for displays towhich the p-Si TFT is applied.

Example 1-25

A glass material prepared to have a composition shown in Example 1-4 wasmelted at 1560-1640° C., followed by refining at 1620-1670° C. and thenstirring at 1440-1530° C., using continuous melting equipment includinga melting bath of fire bricks and a refining bath (adjustment bath) of aplatinum alloy. Thereafter, the glass material was formed into a thinplate having a thickness of 0.7 mm by the overflow downdraw process,followed by cooling at an average rate of 100° C./min within thetemperature range of Tg° C. to Tg−100° C., thereby obtaining a glasssubstrate for liquid crystal displays (or organic EL displays). Notethat the aforementioned properties of the obtained glass substrate weremeasured. Note that, for properties (density, strain point, expansioncoefficient, and Tg) which cannot be measured in the form of asubstrate, the glass substrate was melted again to produce a sampleglass according to the aforementioned sample production process, and theproperties of the sample glass were measured.

The glass substrate of Example 1-25 thus obtained had a meltingtemperature of 1610° C., a β-OH value of 0.20 mm⁻¹, a Tg of 754° C., astrain point of 697° C., and a heat shrinkage rate of 51 ppm, and theother properties thereof were similar to those of Example 1-4. Thus, theglass substrate of Example 1-25 had a Tg of 720° C. or more and amelting temperature of 1680° C. or less, i.e., a high Tg and strainpoint and good meltability. Moreover, the rate of heat shrinkage anddevitrification temperature satisfied the conditions of the first glasssubstrate of the present invention. Note that the glass substrate ofExample 1-25 has a β-OH value which is greater than that of Example 1-4by about 0.1 mm⁻¹, and therefore, has a Tg which is lower than that ofExample 1-4 by 2-3° C., and the Tg is still sufficiently high.Therefore, the glass substrate of Example 1-25 has excellent propertiesand can be used in displays to which the p-Si TFT is applied.

Example 1-26

A glass substrate was produced using a glass material prepared to have aglass composition shown in Example 1-12 in a manner similar to that ofExample 1-25, and the properties of the glass substrate were measured.

The glass substrate of Example 1-26 thus obtained had a meltingtemperature of 1585° C., a β-OH value of 0.21 mm⁻¹, a Tg of 761° C., astrain point of 710° C., and a heat shrinkage rate of 31 ppm, and theother properties thereof were similar to those of Example 1-12. Thus,the glass substrate of Example 1-26 had a Tg of 720° C. or more and amelting temperature of 1680° C. or less, i.e., a high Tg and strainpoint and good meltability. Moreover, the rate of heat shrinkage anddevitrification temperature satisfied the conditions of the first glasssubstrate of the present invention. Note that the glass substrate ofExample 1-26 has a β-OH value which is greater than that of Example 1-12by about 0.1 mm⁻¹, and therefore, has a Tg which is lower than that ofExample 1-12 by 2-3° C., and the Tg is still sufficiently high.Therefore, the glass substrate of Example 1-26 has excellent propertiesand can be used in displays to which the p-Si TFT is applied.

<Second Glass Substrate>

The second glass substrate will be described by way of example. Notethat the second glass substrate includes a glass comprising, asexpressed in mol %;

55-80% SiO₂;

3-20% Al₂O₃;

3-15% B₂O₃; and

3-25% RO (the total amount of MgO, CaO, SrO, and BaO)

wherein

in the glass the contents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfy arelationship (SiO₂+Al₂O₃)/(B₂O₃)=8.45-17.0, and

the devitrification temperature of the glass is 1250° C. or less, and

the rate of heat shrinkage is 60 ppm or less.

Examples and comparative examples of the sample glass having glasscompositions shown in Tables 2-1 and 2-2 were produced in a mannersimilar to that of the examples and comparative examples of the firstglass substrate, and the properties thereof were measured.

TABLE 2-1 Examples 2-1 2-2 2-3 2-4 2-5 2-6 2-7 Composition SiO₂ 71.771.6 70.8 70.5 70.5 70.3 69.4 (mol %) B₂O₃ 6.0 6.0 6.9 7.4 7.4 7.8 8.7Al₂O₃ 11.1 11.1 11.0 10.9 10.9 10.9 10.8 K₂O 0.17 0.17 0.17 0.17 0.40MgO 1.0 CaO 11.1 11.1 11.0 10.9 9.9 10.9 9.8 SrO 0.8 BaO SnO₂ 0.08 0.080.08 0.08 0.08 0.08 0.08 Fe₂O₃ 0.022 0.022 0.022 0.022 (SiO₂ +Al₂O₃)/B₂O₃ 13.8 13.8 11.8 11.0 11.0 10.3 9.2 SiO₂ + Al₂O₃ 82.8 82.681.8 81.4 81.4 81.2 80.2 RO + B₂O₃ + ZnO 17.1 17.1 17.9 18.3 18.3 18.719.3 Al₂O₃/SiO₂ 0.15 0.15 0.15 0.15 0.15 0.15 0.15 RO 11.1 11.1 11.010.9 10.9 10.9 10.6 B₂O₃ + P₂O₅ 6.0 6.0 6.9 7.4 7.4 7.8 8.7 CaO/RO 1 1 11 0.91 1 0.93 SiO₂—Al₂O₃/2 66.1 66.0 65.4 65.0 65.0 64.8 64.1 β-OH 0.110.12 0.11 0.11 0.12 0.13 0.13 Properties devitrification temperature1233 1230 1213 1189 1206 1187 <1140 (° C.) Tg (° C.) 782 776 766 758 751761 741 average coefficient of thermal 34.2 34.0 32.9 32.6 33.1 33.236.3 expansion (×10⁻⁷) (100-300° C.) rate of heat shrinkage (ppm) 31 3644 48 52 46 40 density (g/cm³) 2.41 2.41 2.40 2.39 2.39 2.38 2.40 strainpoint (° C.) 723 716 707 709 704 707 685 melting temperature (° C.) 16441632 1620 1608 1609 1610 1644 liquidus viscosity (log η) 5.0 5.0 5.1 5.25.0 5.2 5.3 specific resistance (Ω · cm) 243 193 194 195 194 248 170(1550° C.) etching rate (μm/h) 65 65 67 69 69 69 72 Examples 2-8 2-92-10 2-11 2-12 2-13 2-14 2-15 Composition SiO₂ 67.2 66.7 69.7 67.5 67.367.8 66.9 67.64 (mol %) B₂O₃ 4.7 5.0 5.0 7.5 8.3 7.8 9.2 7.83 Al₂O₃ 12.513.2 12.2 12.9 12.7 12.5 12.2 12.73 K₂O 0.17 0.17 0.17 0.20 0.17 0.170.17 0.17 MgO 6.9 7.4 5.8 CaO 1.7 1.3 1.42 11.7 11.5 11.5 11.4 6.5 SrO6.8 6.2 5.7 5 BaO SnO₂ 0.09 0.09 0.09 0.10 0.08 0.08 0.08 0.08 Fe₂O₃0.02 0.02 0.02 0.02 0.022 (SiO₂ + Al₂O₃)/B₂O₃ 17.0 16.0 16.4 10.7 9.710.3 8.6 10.3 SiO₂ + Al₂O₃ 79.7 79.9 81.9 80.4 80.0 80.4 79.2 80.4 RO +B₂O₃ + ZnO 20.1 19.9 17.9 19.2 19.8 19.4 20.5 19.4 Al₂O₃/SiO₂ 0.19 0.200.18 0.19 0.19 0.18 0.18 0.19 RO 15.4 14.9 12.9 11.7 11.5 11.5 11.4 11.5B₂O₃ + P₂O₅ 4.7 5.0 5.0 7.5 8.3 7.8 9.2 7.83 CaO/RO 0.11 0.09 0.11 1 1 11 0.57 SiO₂—Al₂O₃/2 61.0 60.1 63.6 61.1 61.0 61.6 60.8 61.3 β-OH 0.130.13 0.14 0.12 0.11 0.11 0.10 0.12 Properties devitrificationtemperature 1241 1219 1215 1230 1220 1236 1193 1221 (° C.) Tg (° C.) 749764 768 763 754 760 741 758 average coefficient of thermal 39.8 36.433.6 36.0 35.9 36.0 36.1 38.2 expansion (×10⁻⁷) (100-300° C.) rate ofheat shrinkage (ppm) 42 29 27 28 33 31 40 33 density (g/cm³) 2.58 2.552.52 2.40 2.41 2.42 2.40 2.48 strain point (° C.) 694 712 711 712 702710 695 703 melting temperature (° C.) 1532 1538 1553 1587 1582 15791567 1595 liquidus viscosity (log η) 4.3 4.5 4.7 4.6 4.7 4.6 4.9 4.8specific resistance (Ω · cm) 203 203 236 137 133 129 142 138 (1550° C.)etching rate (μm/h) 83 85 73 80 82 80 83 83

TABLE 2-2 Examples 2-16 2-17 2-18 2-19 2-20 2-21 2-22 2-23 CompositionSiO₂ 72.0 66.5 66.5 66.5 63.5 70.5 70.5 70.5 (mol %) B₂O₃ 6.4 9.5 9.54.5 4.5 7.4 7.4 7.4 Al₂O₃ 11.4 11.4 12.4 10.4 10.4 10.9 10.9 10.9 K₂O0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 MgO 2.0 CaO 9.9 12.3 11.3 18.321.3 8.9 9.9 8.9 SrO 1.0 2.0 BaO SnO₂ 0.08 0.08 0.08 0.08 0.08 0.08 0.080.08 Fe₂O₃ 0.022 0.022 0.022 0.022 0.022 0.022 0.022 0.022 (SiO₂ +Al₂O₃)/B₂O₃ 13.1 8.2 8.3 16.9 16.2 11.0 11.0 11.0 SiO₂ + Al₂O₃ 83.4 77.978.9 76.9 73.9 81.4 81.4 81.4 RO + B₂O₃ + ZnO 16.3 21.8 20.8 22.8 25.818.3 18.3 18.3 Al₂O₃/SiO₂ 0.16 0.17 0.19 0.16 0.16 0.15 0.15 0.15 RO 9.912.3 11.3 18.3 21.3 10.9 10.9 10.9 B₂O₃ + P₂O₅ 6.4 9.5 9.5 4.5 4.5 7.47.4 7.4 CaO/RO 1 1 1 1 1 0.82 0.91 0.82 SiO₂—Al₂O₃/2 66.3 60.7 60.2 61.258.2 65.0 65.0 65.0 β-OH 0.12 0.11 0.11 0.10 0.10 0.12 0.12 0.12Properties devitrification temperature 1235 1196 1208 1228 1206 12011207 1200 (° C.) Tg (° C.) 781 731 743 739 732 742 752 753 averagecoefficient of 33.3 37.2 36 46.8 50.9 30.4 35.0 35.8 thermal expansion(×10⁻⁷) (100-300° C.) rate of heat shrinkage 23 47 39 49 54 39 34 33(ppm) density (g/cm³) 2.38 2.40 2.40 2.50 2.55 2.38 2.41 2.42 strainpoint (° C.) 731 681 693 689 682 695 702 703 melting temperature (° C.)1640 1554 1560 1548 1541 1614 1610 1608 liquidus viscosity (log η) 4.94.7 4.6 4.3 4.4 5.1 5.0 5.1 specific resistance (Ω · cm) 207 179 191 10873 193 196 197 (1550° C.) etching rate (μm/h) 64 83 85 81 92 69 69 69Comparative Examples 2-1 2-2 2-3 2-4 2-5 2-6 Composition SiO₂ 71.7 71.766.4 67.64 67.64 67.64 (mol %) B₂O₃ 4.0 11.0 7.83 7.83 7.83 Al₂O₃ 11.111.1 10.9 12.73 12.73 12.73 K₂O 0.18 0.17 0.17 0.17 MgO 2.8 1 3 5 CaO13.1 17.1 6.8 10.5 8.5 6.5 SrO 1.69 BaO SnO₂ 0.08 0.09 0.09 0.08 0.080.08 Fe₂O₃ 0.03 0.022 0.022 0.022 (SiO₂ + Al₂O₃)/B₂O₃ 20.7 7.0 10.3 10.310.3 SiO₂ + Al₂O₃ 82.8 82.8 77.4 80.4 80.4 80.4 RO + B₂O₃ + ZnO 17.117.1 22.3 19.4 19.4 19.4 Al₂O₃/SiO₂ 0.15 0.15 0.16 0.19 0.19 0.19 RO13.1 17.1 11.3 11.5 11.5 11.5 B₂O₃ + P₂O₅ 4.0 11.0 7.83 7.83 7.83 CaO/RO1 1 0.60 0.91 0.74 0.57 SiO₂—Al₂O₃/2 66.1 66.1 61.0 61.3 61.3 61.3 β-OH0.13 0.11 0.11 0.11 0.11 0.12 Properties devitrification temperature1282 1330 1196 1260 1294 1324 (° C.) Tg (° C.) 786 826 707 758 749 746average coefficient of 29.8 41.0 34.3 34.4 33.3 32.8 thermal expansion(×10⁻⁷) (100-300° C.) rate of heat shrinkage 17 13 114 32 37 38 (ppm)density (g/cm³) 2.445 2.510 2.40 2.41 2.40 2.40 strain point (° C.) 725774 660 708 697 691 melting temperature (° C.) 1675 1701 1529 1585 15801577 liquidus viscosity (log η) 4.7 4.4 4.6 4.4 4.2 4.0 specificresistance (Ω · cm) 230 188 165 132 130 128 (1550° C.) etching rate(μm/h) 65 65 82 83 81 79

<Third Glass Substrate>

The third glass substrate will be described by way of example. Note thatthe third glass substrate includes a glass comprising, as expressed inmol %,

65-78% SiO₂

3-20% Al₂O₃

3-15% B₂O₃

0% to less than 2% MgO

3.6-16% CaO

0-2% SrO

0% to less than 1% BaO

where

the contents in mol % of B₂O₃, P₂O₅, and CaO satisfy relationshipsB₂O₃+P₂O₅=3-15% and CaO/B₂O₃>1.2,

the strain point of the glass is 665° C. or more, and

the devitrification temperature of the glass is 1250° C. or less.

Examples and comparative examples of the sample glass having glasscompositions shown in Table 3 were produced in a manner similar to thatof the examples and comparative examples of the first glass substrate,and the properties thereof were measured.

TABLE 3 Examples 3-1 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9 3-10 CompositionSiO₂ 71.7 71.6 70.8 70.5 70.5 70.3 67.5 67.3 67.8 66.9 (mol %) B₂O₃ 6.06.0 6.9 7.4 7.4 7.8 7.5 8.3 7.8 9.2 Al₂O₃ 11.1 11.1 11.0 10.9 10.9 10.912.9 12.7 12.5 12.2 K₂O 0.17 0.17 0.17 0.17 0.20 0.17 0.17 0.17 MgO 1.0CaO 11.1 11.1 11.0 10.9 9.9 10.9 11.7 11.5 11.5 11.4 SrO BaO SnO₂ 0.080.08 0.08 0.08 0.08 0.08 0.10 0.08 0.08 0.08 Fe₂O₃ 0.022 0.022 0.0220.022 0.02 0.02 0.02 0.02 (SiO₂ + Al₂O₃)/B₂O₃ 13.8 13.8 11.8 11.0 11.010.3 10.7 9.7 10.3 8.6 SiO₂ + Al₂O₃ 82.8 82.6 81.8 81.4 81.4 81.2 80.480.0 80.4 79.2 RO + B₂O₃ + ZnO 17.1 17.1 17.9 18.3 18.3 18.7 19.2 19.819.4 20.5 Al₂O₃/SiO₂ 0.15 0.15 0.15 0.15 0.15 0.15 0.19 0.19 0.18 0.18RO 11.1 11.1 11.0 10.9 10.9 10.9 11.7 11.5 11.5 11.4 B₂O₃ + P₂O₅ 6.0 6.06.9 7.4 7.4 7.8 7.5 8.3 7.8 9.2 CaO/RO 1 1 1 1 0.91 1 1 1 1 1SiO₂—Al₂O₃/2 66.1 66.0 65.4 65.0 65.0 64.8 61.1 61.0 61.6 60.8 β-OH 0.110.12 0.11 0.11 0.12 0.13 0.12 0.11 0.11 0.10 Properties devitrification1233 1230 1213 1189 1206 1187 1230 1220 1236 1193 temperature (° C.) Tg(° C.) 782 776 766 758 751 761 763 754 760 741 average coefficient 34.234.0 32.9 32.6 33.1 33.2 36.0 35.9 36.0 36.1 of thermal expansion(×10⁻⁷) (100-300° C.) rate of heat 31 36 44 48 52 46 28 33 31 40shrinkage (ppm) density (g/cm³) 2.41 2.41 2.40 2.39 2.39 2.38 2.40 2.412.42 2.40 strain point 723 716 707 709 704 707 712 702 710 695 (° C.)melting temperature 1644 1632 1620 1608 1609 1610 1587 1582 1579 1567 (°C.) liquidus viscosity 5.0 5.0 5.1 5.2 5.0 5.2 4.6 4.7 4.6 4.9 (log η)specific resistance 243 193 194 195 194 248 137 133 129 142 (Ω · cm)(1550° C.) etching rate (μm/h) 65 65 67 69 69 69 80 82 80 83 ExamplesComparative Examples 3-11 3-12 3-13 3-14 3-1 3-2 3-3 3-4 3-5 3-6 Com-SiO₂ 72.0 66.5 70.5 70.5 71.7 71.7 66.4 67.64 67.64 67.64 position B₂O₃6.4 9.5 7.4 7.4 4.0 11.0 7.83 7.83 7.83 (mol %) Al₂O₃ 11.4 11.4 10.910.9 11.1 11.1 10.9 12.73 12.73 12.73 K₂O 0.17 0.17 0.17 0.17 0.18 0.170.17 0.17 MgO 2.8 1 3 5 CaO 9.9 12.3 9.9 8.9 13.1 17.1 6.8 10.5 8.5 6.5SrO 1.0 2.0 1.69 BaO SnO₂ 0.08 0.08 0.08 0.08 0.08 0.09 0.09 0.08 0.080.08 Fe₂O₃ 0.022 0.022 0.022 0.022 0.03 0.022 0.022 0.022 (SiO₂ +Al₂O₃)/ 13.1 8.2 11.0 11.0 20.7 7.0 10.3 10.3 10.3 B₂O₃ SiO₂ + Al₂O₃83.4 77.9 81.4 81.4 82.8 82.8 77.4 80.4 80.4 80.4 RO + B₂O₃ + ZnO 16.321.8 18.3 18.3 17.1 17.1 22.3 19.4 19.4 19.4 Al₂O₃/SiO₂ 0.16 0.17 0.150.15 0.15 0.15 0.16 0.19 0.19 0.19 RO 9.9 12.3 10.9 10.9 13.1 17.1 11.311.5 11.5 11.5 B₂O₃ + P₂O₅ 6.4 9.5 7.4 7.4 4.0 11.0 7.83 7.83 7.83CaO/RO 1 1 0.91 0.82 1 1 0.60 0.91 0.74 0.57 SiO₂—Al₂O₃/2 66.3 60.7 65.065.0 66.1 66.1 61.0 61.3 61.3 61.3 β-OH 0.12 0.11 0.12 0.12 0.13 0.110.11 0.11 0.11 0.12 Properties devitrification 1235 1196 1207 1200 12821330 1196 1260 1294 1324 temperature (° C.) Tg (° C.) 781 731 752 753786 826 707 758 749 746 average coefficient 33.3 37.2 35.0 35.8 29.841.0 34.3 34.4 33.3 32.8 of thermal expansion (×10⁻⁷) (100-300° C.) rateof heat 23 47 34 33 17 13 114 32 37 38 shrinkage (ppm) density (g/cm³)2.38 2.40 2.41 2.42 2.445 2.510 2.40 2.41 2.40 2.40 strain point 731 681702 703 725 774 660 708 697 691 (° C.) melting temperature 1640 15541610 1608 1675 1701 1529 1585 1580 1577 (° C.) liquidus viscosity 4.94.7 5.0 5.1 4.7 4.4 4.6 4.4 4.2 4.0 (log η) specific resistance 207 179196 197 230 188 165 132 130 128 (Ω · cm) (1550° C.) etching rate (μm/h)64 83 69 69 65 65 82 83 81 79

<Fourth Glass Substrate>

The fourth glass substrate will be described by way of example. Notethat the fourth glass substrate includes a glass comprising, asexpressed in mol %,

65-78% SiO₂

3-20% Al₂O₃

3-9.5% B₂O₃

0% to less than 2% MgO

3.6-16% CaO

0-2% SrO

substantially no BaO

where

the contents in mol % of B₂O₃, P₂O₅, and CaO satisfy relationshipsB₂O₃+P₂O₅=3-9.5% and CaO/B₂O₃>1.2, and

the devitrification temperature of the glass is 1250° C. or less.

Examples and comparative examples of the sample glass having glasscompositions shown in Table 4 were produced in a manner similar to thatof the examples and comparative examples of the first glass substrate,and the properties thereof were measured.

TABLE 4 Examples 4-1 4-2 4-3 4-4 4-5 4-6 4-7 4-8 4-9 4-10 CompositionSiO₂ 71.7 71.6 70.8 70.5 70.5 70.3 67.5 67.3 67.8 66.9 (mol %) B₂O₃ 6.06.0 6.9 7.4 7.4 7.8 7.5 8.3 7.8 9.2 Al₂O₃ 11.1 11.1 11.0 10.9 10.9 10.912.9 12.7 12.5 12.2 K₂O 0.17 0.17 0.17 0.17 0.20 0.17 0.17 0.17 MgO 1.0CaO 11.1 11.1 11.0 10.9 9.9 10.9 11.7 11.5 11.5 11.4 SrO BaO SnO₂ 0.080.08 0.08 0.08 0.08 0.08 0.10 0.08 0.08 0.08 Fe₂O₃ 0.022 0.022 0.0220.022 0.02 0.02 0.02 0.02 (SiO₂ + Al₂O₃)/B₂O₃ 13.8 13.8 11.8 11.0 11.010.3 10.7 9.7 10.3 8.6 SiO₂ + Al₂O₃ 82.8 82.6 81.8 81.4 81.4 81.2 80.480.0 80.4 79.2 RO + B₂O₃ + ZnO 17.1 17.1 17.9 18.3 18.3 18.7 19.2 19.819.4 20.5 Al₂O₃/SiO₂ 0.15 0.15 0.15 0.15 0.15 0.15 0.19 0.19 0.18 0.18RO 11.1 11.1 11.0 10.9 10.9 10.9 11.7 11.5 11.5 11.4 B₂O₃ + P₂O₅ 6.0 6.06.9 7.4 7.4 7.8 7.5 8.3 7.8 9.2 CaO/RO 1 1 1 1 0.91 1 1 1 1 1SiO₂—Al₂O₃/2 66.1 66.0 65.4 65.0 65.0 64.8 61.1 61.0 61.6 60.8 β-OH 0.110.12 0.11 0.11 0.12 0.13 0.12 0.11 0.11 0.10 Properties devitrificationtemperature 1233 1230 1213 1189 1206 1187 1230 1220 1236 1193 (° C.) Tg(° C.) 782 776 766 758 751 761 763 754 760 741 average coefficient ofthermal 34.2 34.0 32.9 32.6 33.1 33.2 36.0 35.9 36.0 36.1 expansion(×10⁻⁷) (100-300° C.) rate of heat shrinkage (ppm) 31 36 44 48 52 46 2833 31 40 density (g/cm³) 2.41 2.41 2.40 2.39 2.39 2.38 2.40 2.41 2.422.40 strain point (° C.) 723 716 707 709 704 707 712 702 710 695 meltingtemperature (° C.) 1644 1632 1620 1608 1609 1610 1587 1582 1579 1567liquidus viscosity (log η) 5.0 5.0 5.1 5.2 5.0 5.2 4.6 4.7 4.6 4.9specific resistance (Ω · cm) 243 193 194 195 194 248 137 133 129 142(1550° C.) etching rate (μm/h) 65 65 67 69 69 69 80 82 80 83 ExamplesComparative Examples 4-11 4-12 4-13 4-1 4-2 4-3 4-4 4-5 4-6 CompositionSiO₂ 72.0 70.5 70.5 71.7 71.7 66.4 67.64 67.64 67.64 (mol %) B₂O₃ 6.47.4 7.4 4.0 11.0 7.83 7.83 7.83 Al₂O₃ 11.4 10.9 10.9 11.1 11.1 10.912.73 12.73 12.73 K₂O 0.17 0.17 0.17 0.18 0.17 0.17 0.17 MgO 2.8 1 3 5CaO 9.9 9.9 8.9 13.1 17.1 6.8 10.5 8.5 6.5 SrO 1.0 2.0 1.69 BaO SnO₂0.08 0.08 0.08 0.08 0.09 0.09 0.08 0.08 0.08 Fe₂O₃ 0.022 0.022 0.0220.03 0.022 0.022 0.022 (SiO₂ + Al₂O₃)/B₂O₃ 13.1 11.0 11.0 20.7 7.0 10.310.3 10.3 SiO₂ + Al₂O₃ 83.4 81.4 81.4 82.8 82.8 77.4 80.4 80.4 80.4 RO +B₂O₃ + ZnO 16.3 18.3 18.3 17.1 17.1 22.3 19.4 19.4 19.4 Al₂O₃/SiO₂ 0.160.15 0.15 0.15 0.15 0.16 0.19 0.19 0.19 RO 9.9 10.9 10.9 13.1 17.1 11.311.5 11.5 11.5 B₂O₃ + P₂O₅ 6.4 7.4 7.4 4.0 11.0 7.83 7.83 7.83 CaO/RO 10.91 0.82 1 1 0.60 0.91 0.74 0.57 SiO₂—Al₂O₃/2 66.3 65.0 65.0 66.1 66.161.0 61.3 61.3 61.3 β-OH 0.12 0.12 0.12 0.13 0.11 0.11 0.11 0.11 0.12Properties devitrification temperature 1235 1207 1200 1282 1330 11961260 1294 1324 (° C.) Tg (° C.) 781 752 753 786 826 707 758 749 746average coefficient of thermal 33.3 35.0 35.8 29.8 41.0 34.3 34.4 33.332.8 expansion (×10⁻⁷) (100-300° C.) rate of heat shrinkage (ppm) 23 3433 17 13 114 32 37 38 density (g/cm³) 2.38 2.41 2.42 2.445 2.510 2.402.41 2.40 2.40 strain point (° C.) 731 702 703 725 774 660 708 697 691melting temperature (° C.) 1640 1610 1608 1675 1701 1529 1585 1580 1577liquidus viscosity (log η) 4.9 5.0 5.1 4.7 4.4 4.6 4.4 4.2 4.0 specificresistance (Ω · cm) 207 196 197 230 188 165 132 130 128 (1550° C.)etching rate (μm/h) 64 69 69 65 65 82 83 81 79

The flat panel display glass substrate of the present invention issuitable for flat panel displays in which the p-Si is used, and isparticularly suitable as a glass substrate for liquid crystal displaysand organic EL displays in which the p-Si TFT is used. The flat paneldisplay glass substrate of the present invention is suitable as adisplay glass substrate for mobile terminals for which a high resolutionis required, among other things.

Note that the specific embodiments or examples described in the“DETAILED DESCRIPTION OF THE INVENTION” section are only for the purposeof illustrating the technical aspects of the present invention, and arenot to be construed in a narrow sense by limiting the present inventionto such specific examples. Various changes and modifications can be madewithout departing from the spirit and scope of the present invention asset forth in the following claims.

What is claimed is:
 1. A method for manufacturing a display glasssubstrate, the method comprising: a melting step of melting a glassmaterial for a glass comprising, as expressed in mol %, 55-80% SiO₂,3-20% Al₂O₃, 3-15% B₂O₃, and 3-25% RO (the total amount of MgO, CaO,SrO, and BaO), with the contents in mol % of SiO₂, Al₂O₃, and B₂O₃satisfying a relationship (SiO₂+Al₂O₃)/(B₂O₃)=7.5-17, the strain pointof the glass being 685° C. or more, and the devitrification temperatureof the glass being 1250° C. or less, to produce a molten glass; aforming step of forming the molten glass into a glass plate; and anannealing step of annealing the glass plate, wherein the glass plate hasa rate of heat shrinkage of 75 ppm or less, and the rate of heatshrinkage is calculated from the amount of shrinkage of the glass platemeasured after a heat treatment which is performed at a rising andfalling temperature rate of 10° C./min and at 550° C. for 2 hours by:the rate of heat shrinkage (ppm)={the amount of shrinkage of the glasssubstrate after the heat treatment/the length of the glass substratebefore the heat treatment}×10⁶.
 2. The method for manufacturing adisplay glass substrate according to claim 1, wherein in the meltingstep, the molten glass is produced to have a β-OH of 0.05-0.40 mm⁻¹. 3.The method for manufacturing a display glass substrate according toclaim 1, wherein in the annealing step, the glass plate is cooled at anaverage rate of 50-300° C./min within the temperature range of the glasstransition temperature (Tg) to Tg−100° C.
 4. The method formanufacturing a display glass substrate according to claim 1, wherein inthe glass, the contents in mol % of SrO and BaO satisfy SrO+BaO=0-5%. 5.A method for manufacturing a display glass substrate, the methodcomprising: a melting step of melting a glass material for a glasscomprising, as expressed in mol %, 55-80% SiO₂, 3-20% Al₂O₃, 3-15% B₂O₃,and 3-25% RO (the total amount of MgO, CaO, SrO, and BaO), with thecontents in mol % of SiO₂, Al₂O₃, and B₂O₃ satisfying a relationship(SiO₂+Al₂O₃)/(B₂O₃)=8.45-17.0, the strain point of the glass being 685°C. or more, and the devitrification temperature of the glass being 1250°C. or less, to produce a molten glass; a forming step of forming themolten glass into a glass plate; and an annealing step of annealing theglass plate, wherein the glass plate has a rate of heat shrinkage of 60ppm or less, and the rate of heat shrinkage is calculated from theamount of shrinkage of the glass plate measured after a heat treatmentwhich is performed at a rising and falling temperature rate of 10°C./min and at 550° C. for 2 hours by:the rate of heat shrinkage (ppm)={the amount of shrinkage of the glassplate after the heat treatment/the length of the glass plate before theheat treatment}×10⁶.
 6. The method for manufacturing a display glasssubstrate according to claim 5, wherein in the melting step, the moltenglass is produced to have a β-OH of 0.05-0.40 mm⁻¹.
 7. The method formanufacturing a display glass substrate according to claim 5, wherein inthe annealing step, the glass plate is cooled at an average rate of50-300° C./min within the temperature range of the glass transitiontemperature (Tg) to Tg−100° C.
 8. The method for manufacturing a displayglass substrate according to claim 5, wherein in the glass, the contentsin mol % of SrO and BaO satisfy SrO+BaO=0-5%.